Add CODEOWNERS

perf(proxy): Add HTTP client reuse and buffer pooling

.github/CODEOWNERS

@@ -0,0 +1 @@
+* @oschwartz10612 @miloschwartz

.github/workflows/test.yml

@@ -19,7 +19,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@4b73464bb391d4059bd26b0524d20df3927bd417 # v6.3.0
         with:
-          go-version: 1.25
+          go-version: 1.26
 
       - name: Build go
         run: go build

README.md

@@ -40,6 +40,24 @@ The PROXY protocol allows downstream proxies to know the real client IP address
 
 In single node (self hosted) Pangolin deployments this can be bypassed by using port 443:443 to route to Traefik instead of the SNI proxy at 8443.
 
+### Observability with OpenTelemetry
+
+Gerbil includes comprehensive OpenTelemetry metrics instrumentation for monitoring and observability. Metrics can be exported via:
+
+- **Prometheus**: Pull-based metrics at the `/metrics` endpoint (enabled by default)
+- **OTLP**: Push-based metrics to any OpenTelemetry-compatible collector
+
+Key metrics include:
+
+- WireGuard interface and peer status
+- Bandwidth usage per peer
+- Active relay sessions and proxy connections
+- Handshake success/failure rates
+- Route lookup cache hit/miss ratios
+- Go runtime metrics (GC, goroutines, memory)
+
+See [docs/observability.md](docs/observability.md) for complete documentation, metrics reference, and examples.
+
 ## CLI Args
 
 Important:

docs/observability.md

@@ -0,0 +1,269 @@
+<!-- markdownlint-disable MD036 MD060 -->
+# Gerbil Observability Architecture
+
+This document describes the metrics subsystem for Gerbil, explains the design
+decisions, and shows how to configure each backend.
+
+---
+
+## Architecture Overview
+
+Gerbil's metrics subsystem uses a **pluggable backend** design:
+
+```text
+main.go  ─── internal/metrics  ─── internal/observability  ─── backend
+                 (facade)                 (interface)           Prometheus
+                                                           OR   OTel/OTLP
+                                                           OR   Noop (disabled)
+```
+
+Application code (main, relay, proxy) calls only the `metrics.Record*`
+functions in `internal/metrics`. That package delegates to whichever backend
+was selected at startup via `internal/observability.Backend`.
+
+### Why Prometheus-native and OTel are mutually exclusive
+
+**Exactly one** metrics backend may be active at runtime:
+
+| Mode | What happens |
+|------|-------------|
+| `prometheus` | Native Prometheus client registers metrics on a dedicated registry and exposes `/metrics`. No OTel SDK is initialised. |
+| `otel` | OTel SDK pushes metrics via OTLP/gRPC or OTLP/HTTP to an external collector. No `/metrics` endpoint is exposed. |
+| `none` | A safe noop backend is used. All `Record*` calls are discarded. |
+
+Running both simultaneously would mean every metric is recorded twice through
+two different code paths, with differing semantics (pull vs. push, different
+naming rules, different cardinality handling). The design enforces a single
+source of truth.
+
+### Future OTel tracing and logging
+
+The `internal/observability/otel/` package is designed so that tracing and
+logging support can be added **beside** the existing metrics code without
+touching the Prometheus-native path:
+
+```bash
+internal/observability/otel/
+  backend.go     ← metrics
+  exporter.go    ← OTLP exporter creation
+  resource.go    ← OTel resource
+  trace.go       ← future: TracerProvider setup
+  log.go         ← future: LoggerProvider setup
+```
+
+---
+
+## Configuration
+
+### Config precedence
+
+1. CLI flags (highest priority)
+2. Environment variables
+3. Defaults
+
+### Config struct
+
+```go
+type MetricsConfig struct {
+    Enabled               bool
+    Backend               string // "prometheus" | "otel" | "none"
+    Prometheus            PrometheusConfig
+    OTel                  OTelConfig
+    ServiceName           string
+    ServiceVersion        string
+    DeploymentEnvironment string
+}
+
+type PrometheusConfig struct {
+    Path string // default: "/metrics"
+}
+
+type OTelConfig struct {
+    Protocol       string        // "grpc" (default) or "http"
+    Endpoint       string        // default: "localhost:4317"
+    Insecure       bool          // default: true
+    ExportInterval time.Duration // default: 60s
+}
+```
+
+### Environment variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `METRICS_ENABLED` | `true` | Enable/disable metrics |
+| `METRICS_BACKEND` | `prometheus` | Backend: `prometheus`, `otel`, or `none` |
+| `METRICS_PATH` | `/metrics` | HTTP path for Prometheus endpoint |
+| `OTEL_METRICS_PROTOCOL` | `grpc` | OTLP transport: `grpc` or `http` |
+| `OTEL_METRICS_ENDPOINT` | `localhost:4317` | OTLP collector address |
+| `OTEL_METRICS_INSECURE` | `true` | Disable TLS for OTLP |
+| `OTEL_METRICS_EXPORT_INTERVAL` | `60s` | Push interval (e.g. `10s`, `1m`) |
+| `DEPLOYMENT_ENVIRONMENT` | _(unset)_ | OTel deployment.environment attribute |
+
+### CLI flags
+
+```bash
+--metrics-enabled            bool    (default: true)
+--metrics-backend            string  (default: prometheus)
+--metrics-path               string  (default: /metrics)
+--otel-metrics-protocol      string  (default: grpc)
+--otel-metrics-endpoint      string  (default: localhost:4317)
+--otel-metrics-insecure      bool    (default: true)
+--otel-metrics-export-interval  duration  (default: 1m0s)
+```
+
+---
+
+## When to choose each backend
+
+| Criterion | Prometheus | OTel/OTLP |
+|-----------|-----------|-----------|
+| Existing Prometheus/Grafana stack | ✅ | |
+| Pull-based scraping | ✅ | |
+| No external collector required | ✅ | |
+| Vendor-neutral telemetry | | ✅ |
+| Push-based export | | ✅ |
+| Grafana Cloud / managed OTLP | | ✅ |
+| Future traces + logs via same pipeline | | ✅ |
+
+---
+
+## Enabling Prometheus-native mode
+
+### Environment variables
+
+```bash
+METRICS_ENABLED=true
+METRICS_BACKEND=prometheus
+METRICS_PATH=/metrics
+```
+
+### CLI
+
+```bash
+./gerbil --metrics-enabled --metrics-backend=prometheus --metrics-path=/metrics \
+         --config=/etc/gerbil/config.json
+```
+
+The metrics config is supplied separately via env/flags; it is not embedded
+in the WireGuard config file.
+
+The Prometheus `/metrics` endpoint is registered only when
+`--metrics-backend=prometheus`. All gerbil_* metrics plus Go runtime metrics
+are available.
+
+---
+
+## Enabling OTel mode
+
+### Environment variables
+
+```bash
+export METRICS_ENABLED=true
+export METRICS_BACKEND=otel
+export OTEL_METRICS_PROTOCOL=grpc
+export OTEL_METRICS_ENDPOINT=otel-collector:4317
+export OTEL_METRICS_INSECURE=true
+export OTEL_METRICS_EXPORT_INTERVAL=10s
+export DEPLOYMENT_ENVIRONMENT=production
+```
+
+### CLI
+
+```bash
+./gerbil --metrics-enabled \
+         --metrics-backend=otel \
+         --otel-metrics-protocol=grpc \
+         --otel-metrics-endpoint=otel-collector:4317 \
+         --otel-metrics-insecure \
+         --otel-metrics-export-interval=10s \
+         --config=/etc/gerbil/config.json
+```
+
+### HTTP mode (OTLP/HTTP)
+
+```bash
+export OTEL_METRICS_PROTOCOL=http
+export OTEL_METRICS_ENDPOINT=otel-collector:4318
+```
+
+---
+
+## Disabling metrics
+
+```bash
+export METRICS_ENABLED=false
+# or
+./gerbil --metrics-enabled=false
+# or
+./gerbil --metrics-backend=none
+```
+
+When disabled, all `Record*` calls are directed to a safe noop backend that
+discards observations without allocating or locking.
+
+---
+
+## Metric catalog
+
+All metrics use the prefix `gerbil_<component>_<name>`.
+
+### WireGuard metrics
+
+| Metric | Type | Labels | Description |
+|--------|------|--------|-------------|
+| `gerbil_wg_interface_up` | Gauge | `ifname`, `instance` | 1=up, 0=down |
+| `gerbil_wg_peers_total` | UpDownCounter | `ifname` | Configured peers |
+| `gerbil_wg_peer_connected` | Gauge | `ifname`, `peer` | 1=connected, 0=disconnected |
+| `gerbil_wg_bytes_received_total` | Counter | `ifname`, `peer` | Bytes received |
+| `gerbil_wg_bytes_transmitted_total` | Counter | `ifname`, `peer` | Bytes transmitted |
+| `gerbil_wg_handshakes_total` | Counter | `ifname`, `peer`, `result` | Handshake attempts |
+| `gerbil_wg_handshake_latency_seconds` | Histogram | `ifname`, `peer` | Handshake duration |
+| `gerbil_wg_peer_rtt_seconds` | Histogram | `ifname`, `peer` | Peer round-trip time |
+
+### Relay metrics
+
+| Metric | Type | Labels |
+|--------|------|--------|
+| `gerbil_proxy_mapping_active` | UpDownCounter | `ifname` |
+| `gerbil_session_active` | UpDownCounter | `ifname` |
+| `gerbil_active_sessions` | UpDownCounter | `ifname` |
+| `gerbil_udp_packets_total` | Counter | `ifname`, `type`, `direction` |
+| `gerbil_hole_punch_events_total` | Counter | `ifname`, `result` |
+
+### SNI proxy metrics
+
+| Metric | Type | Labels |
+|--------|------|--------|
+| `gerbil_sni_connections_total` | Counter | `result` |
+| `gerbil_sni_active_connections` | UpDownCounter | _(none)_ |
+| `gerbil_sni_route_cache_hits_total` | Counter | `result` |
+| `gerbil_sni_route_api_requests_total` | Counter | `result` |
+| `gerbil_proxy_route_lookups_total` | Counter | `result`, `hostname` |
+
+### HTTP metrics
+
+| Metric | Type | Labels |
+|--------|------|--------|
+| `gerbil_http_requests_total` | Counter | `endpoint`, `method`, `status_code` |
+| `gerbil_http_request_duration_seconds` | Histogram | `endpoint`, `method` |
+
+---
+
+## Using Docker Compose
+
+The `docker-compose.metrics.yml` provides a complete observability stack.
+
+**Prometheus mode:**
+
+```bash
+METRICS_BACKEND=prometheus docker-compose -f docker-compose.metrics.yml up -d
+# Scrape at http://localhost:3003/metrics
+# Grafana at http://localhost:3000 (admin/admin)
+```
+
+**OTel mode:**
+
+```bash
+METRICS_BACKEND=otel OTEL_METRICS_ENDPOINT=otel-collector:4317 \
+  docker-compose -f docker-compose.metrics.yml up -d
+```

examples/otel-collector-config.yaml

@@ -0,0 +1,46 @@
+receivers:
+  otlp:
+    protocols:
+      grpc:
+        endpoint: 0.0.0.0:4317
+      http:
+        endpoint: 0.0.0.0:4318
+
+processors:
+  batch:
+    timeout: 10s
+    send_batch_size: 1024
+  
+  # Add resource attributes
+  resource:
+    attributes:
+      - key: service.environment
+        value: "development"
+        action: insert
+
+exporters:
+  # Prometheus exporter for scraping
+  prometheus:
+    endpoint: "0.0.0.0:8889"
+    namespace: "gerbil"
+    send_timestamps: true
+    metric_expiration: 5m
+    resource_to_telemetry_conversion:
+      enabled: true
+
+  # Prometheus remote write (optional)
+  prometheusremotewrite:
+    endpoint: "http://prometheus:9090/api/v1/write"
+    tls:
+      insecure: true
+  
+  # Debug exporter for debugging
+  debug:
+    verbosity: normal
+
+service:
+  pipelines:
+    metrics:
+      receivers: [otlp]
+      processors: [batch, resource]
+      exporters: [prometheus, prometheusremotewrite, debug]

examples/prometheus.yml

@@ -0,0 +1,24 @@
+global:
+  scrape_interval: 15s
+  evaluation_interval: 15s
+  external_labels:
+    cluster: 'gerbil-dev'
+
+scrape_configs:
+  # Scrape Gerbil's /metrics endpoint directly
+  - job_name: 'gerbil'
+    static_configs:
+      - targets: ['gerbil:3003']
+        labels:
+          service: 'gerbil'
+          environment: 'development'
+
+  # Scrape OpenTelemetry Collector metrics
+  - job_name: 'otel-collector'
+    static_configs:
+      - targets: ['otel-collector:8888']
+        labels:
+          service: 'otel-collector'
+      - targets: ['otel-collector:8889']
+        labels:
+          service: 'otel-collector-prometheus-exporter'

go.mod

@@ -4,20 +4,47 @@ go 1.26.0
 
 require (
 	github.com/patrickmn/go-cache v2.1.0+incompatible
+	github.com/prometheus/client_golang v1.20.5
 	github.com/vishvananda/netlink v1.3.1
+	go.opentelemetry.io/otel v1.42.0
+	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.42.0
+	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.42.0
+	go.opentelemetry.io/otel/metric v1.42.0
+	go.opentelemetry.io/otel/sdk v1.42.0
+	go.opentelemetry.io/otel/sdk/metric v1.42.0
 	golang.org/x/crypto v0.49.0
 	golang.org/x/sync v0.20.0
 	golang.zx2c4.com/wireguard/wgctrl v0.0.0-20230429144221-925a1e7659e6
 )
 
 require (
-	github.com/google/go-cmp v0.5.9 // indirect
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cenkalti/backoff/v5 v5.0.3 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/go-logr/logr v1.4.3 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/google/go-cmp v0.7.0 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/grpc-ecosystem/grpc-gateway/v2 v2.28.0 // indirect
 	github.com/josharian/native v1.1.0 // indirect
+	github.com/klauspost/compress v1.17.9 // indirect
 	github.com/mdlayher/genetlink v1.3.2 // indirect
 	github.com/mdlayher/netlink v1.7.2 // indirect
 	github.com/mdlayher/socket v0.4.1 // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
+	github.com/prometheus/client_model v0.6.1 // indirect
+	github.com/prometheus/common v0.61.0 // indirect
+	github.com/prometheus/procfs v0.15.1 // indirect
 	github.com/vishvananda/netns v0.0.5 // indirect
+	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
+	go.opentelemetry.io/otel/trace v1.42.0 // indirect
+	go.opentelemetry.io/proto/otlp v1.9.0 // indirect
 	golang.org/x/net v0.51.0 // indirect
 	golang.org/x/sys v0.42.0 // indirect
+	golang.org/x/text v0.35.0 // indirect
 	golang.zx2c4.com/wireguard v0.0.0-20230325221338-052af4a8072b // indirect
+	google.golang.org/genproto/googleapis/api v0.0.0-20260209200024-4cfbd4190f57 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20260209200024-4cfbd4190f57 // indirect
+	google.golang.org/grpc v1.79.3 // indirect
+	google.golang.org/protobuf v1.36.11 // indirect
 )

go.sum

@@ -1,7 +1,30 @@
-github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
-github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
+github.com/cenkalti/backoff/v5 v5.0.3 h1:ZN+IMa753KfX5hd8vVaMixjnqRZ3y8CuJKRKj1xcsSM=
+github.com/cenkalti/backoff/v5 v5.0.3/go.mod h1:rkhZdG3JZukswDf7f0cwqPNk4K0sa+F97BxZthm/crw=
+github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
+github.com/go-logr/logr v1.4.3 h1:CjnDlHq8ikf6E492q6eKboGOC0T8CDaOvkHCIg8idEI=
+github.com/go-logr/logr v1.4.3/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
+github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
+github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
+github.com/golang/protobuf v1.5.4 h1:i7eJL8qZTpSEXOPTxNKhASYpMn+8e5Q6AdndVa1dWek=
+github.com/golang/protobuf v1.5.4/go.mod h1:lnTiLA8Wa4RWRcIUkrtSVa5nRhsEGBg48fD6rSs7xps=
+github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
+github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
+github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
+github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/grpc-ecosystem/grpc-gateway/v2 v2.28.0 h1:HWRh5R2+9EifMyIHV7ZV+MIZqgz+PMpZ14Jynv3O2Zs=
+github.com/grpc-ecosystem/grpc-gateway/v2 v2.28.0/go.mod h1:JfhWUomR1baixubs02l85lZYYOm7LV6om4ceouMv45c=
 github.com/josharian/native v1.1.0 h1:uuaP0hAbW7Y4l0ZRQ6C9zfb7Mg1mbFKry/xzDAfmtLA=
 github.com/josharian/native v1.1.0/go.mod h1:7X/raswPFr05uY3HiLlYeyQntB6OO7E/d2Cu7qoaN2w=
+github.com/klauspost/compress v1.17.9 h1:6KIumPrER1LHsvBVuDa0r5xaG0Es51mhhB9BQB2qeMA=
+github.com/klauspost/compress v1.17.9/go.mod h1:Di0epgTjJY877eYKx5yC51cX2A2Vl2ibi7bDH9ttBbw=
+github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=
+github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
 github.com/mdlayher/genetlink v1.3.2 h1:KdrNKe+CTu+IbZnm/GVUMXSqBBLqcGpRDa0xkQy56gw=
 github.com/mdlayher/genetlink v1.3.2/go.mod h1:tcC3pkCrPUGIKKsCsp0B3AdaaKuHtaxoJRz3cc+528o=
 github.com/mdlayher/netlink v1.7.2 h1:/UtM3ofJap7Vl4QWCPDGXY8d3GIY2UGSDbK+QWmY8/g=
@@ -10,12 +33,44 @@ github.com/mdlayher/socket v0.4.1 h1:eM9y2/jlbs1M615oshPQOHZzj6R6wMT7bX5NPiQvn2U
 github.com/mdlayher/socket v0.4.1/go.mod h1:cAqeGjoufqdxWkD7DkpyS+wcefOtmu5OQ8KuoJGIReA=
 github.com/mikioh/ipaddr v0.0.0-20190404000644-d465c8ab6721 h1:RlZweED6sbSArvlE924+mUcZuXKLBHA35U7LN621Bws=
 github.com/mikioh/ipaddr v0.0.0-20190404000644-d465c8ab6721/go.mod h1:Ickgr2WtCLZ2MDGd4Gr0geeCH5HybhRJbonOgQpvSxc=
+github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
+github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
 github.com/patrickmn/go-cache v2.1.0+incompatible h1:HRMgzkcYKYpi3C8ajMPV8OFXaaRUnok+kx1WdO15EQc=
 github.com/patrickmn/go-cache v2.1.0+incompatible/go.mod h1:3Qf8kWWT7OJRJbdiICTKqZju1ZixQ/KpMGzzAfe6+WQ=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/prometheus/client_golang v1.20.5 h1:cxppBPuYhUnsO6yo/aoRol4L7q7UFfdm+bR9r+8l63Y=
+github.com/prometheus/client_golang v1.20.5/go.mod h1:PIEt8X02hGcP8JWbeHyeZ53Y/jReSnHgO035n//V5WE=
+github.com/prometheus/client_model v0.6.1 h1:ZKSh/rekM+n3CeS952MLRAdFwIKqeY8b62p8ais2e9E=
+github.com/prometheus/client_model v0.6.1/go.mod h1:OrxVMOVHjw3lKMa8+x6HeMGkHMQyHDk9E3jmP2AmGiY=
+github.com/prometheus/common v0.61.0 h1:3gv/GThfX0cV2lpO7gkTUwZru38mxevy90Bj8YFSRQQ=
+github.com/prometheus/common v0.61.0/go.mod h1:zr29OCN/2BsJRaFwG8QOBr41D6kkchKbpeNH7pAjb/s=
+github.com/prometheus/procfs v0.15.1 h1:YagwOFzUgYfKKHX6Dr+sHT7km/hxC76UB0learggepc=
+github.com/prometheus/procfs v0.15.1/go.mod h1:fB45yRUv8NstnjriLhBQLuOUt+WW4BsoGhij/e3PBqk=
+github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
+github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 github.com/vishvananda/netlink v1.3.1 h1:3AEMt62VKqz90r0tmNhog0r/PpWKmrEShJU0wJW6bV0=
 github.com/vishvananda/netlink v1.3.1/go.mod h1:ARtKouGSTGchR8aMwmkzC0qiNPrrWO5JS/XMVl45+b4=
 github.com/vishvananda/netns v0.0.5 h1:DfiHV+j8bA32MFM7bfEunvT8IAqQ/NzSJHtcmW5zdEY=
 github.com/vishvananda/netns v0.0.5/go.mod h1:SpkAiCQRtJ6TvvxPnOSyH3BMl6unz3xZlaprSwhNNJM=
+go.opentelemetry.io/auto/sdk v1.2.1 h1:jXsnJ4Lmnqd11kwkBV2LgLoFMZKizbCi5fNZ/ipaZ64=
+go.opentelemetry.io/auto/sdk v1.2.1/go.mod h1:KRTj+aOaElaLi+wW1kO/DZRXwkF4C5xPbEe3ZiIhN7Y=
+go.opentelemetry.io/otel v1.42.0 h1:lSQGzTgVR3+sgJDAU/7/ZMjN9Z+vUip7leaqBKy4sho=
+go.opentelemetry.io/otel v1.42.0/go.mod h1:lJNsdRMxCUIWuMlVJWzecSMuNjE7dOYyWlqOXWkdqCc=
+go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.42.0 h1:MdKucPl/HbzckWWEisiNqMPhRrAOQX8r4jTuGr636gk=
+go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.42.0/go.mod h1:RolT8tWtfHcjajEH5wFIZ4Dgh5jpPdFXYV9pTAk/qjc=
+go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.42.0 h1:H7O6RlGOMTizyl3R08Kn5pdM06bnH8oscSj7o11tmLA=
+go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.42.0/go.mod h1:mBFWu/WOVDkWWsR7Tx7h6EpQB8wsv7P0Yrh0Pb7othc=
+go.opentelemetry.io/otel/metric v1.42.0 h1:2jXG+3oZLNXEPfNmnpxKDeZsFI5o4J+nz6xUlaFdF/4=
+go.opentelemetry.io/otel/metric v1.42.0/go.mod h1:RlUN/7vTU7Ao/diDkEpQpnz3/92J9ko05BIwxYa2SSI=
+go.opentelemetry.io/otel/sdk v1.42.0 h1:LyC8+jqk6UJwdrI/8VydAq/hvkFKNHZVIWuslJXYsDo=
+go.opentelemetry.io/otel/sdk v1.42.0/go.mod h1:rGHCAxd9DAph0joO4W6OPwxjNTYWghRWmkHuGbayMts=
+go.opentelemetry.io/otel/sdk/metric v1.42.0 h1:D/1QR46Clz6ajyZ3G8SgNlTJKBdGp84q9RKCAZ3YGuA=
+go.opentelemetry.io/otel/sdk/metric v1.42.0/go.mod h1:Ua6AAlDKdZ7tdvaQKfSmnFTdHx37+J4ba8MwVCYM5hc=
+go.opentelemetry.io/otel/trace v1.42.0 h1:OUCgIPt+mzOnaUTpOQcBiM/PLQ/Op7oq6g4LenLmOYY=
+go.opentelemetry.io/otel/trace v1.42.0/go.mod h1:f3K9S+IFqnumBkKhRJMeaZeNk9epyhnCmQh/EysQCdc=
+go.opentelemetry.io/proto/otlp v1.9.0 h1:l706jCMITVouPOqEnii2fIAuO3IVGBRPV5ICjceRb/A=
+go.opentelemetry.io/proto/otlp v1.9.0/go.mod h1:xE+Cx5E/eEHw+ISFkwPLwCZefwVjY+pqKg1qcK03+/4=
 golang.org/x/crypto v0.49.0 h1:+Ng2ULVvLHnJ/ZFEq4KdcDd/cfjrrjjNSXNzxg0Y4U4=
 golang.org/x/crypto v0.49.0/go.mod h1:ErX4dUh2UM+CFYiXZRTcMpEcN8b/1gxEuv3nODoYtCA=
 golang.org/x/net v0.51.0 h1:94R/GTO7mt3/4wIKpcR5gkGmRLOuE/2hNGeWq/GBIFo=
@@ -26,7 +81,21 @@ golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.42.0 h1:omrd2nAlyT5ESRdCLYdm3+fMfNFE/+Rf4bDIQImRJeo=
 golang.org/x/sys v0.42.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/text v0.35.0 h1:JOVx6vVDFokkpaq1AEptVzLTpDe9KGpj5tR4/X+ybL8=
+golang.org/x/text v0.35.0/go.mod h1:khi/HExzZJ2pGnjenulevKNX1W67CUy0AsXcNubPGCA=
 golang.zx2c4.com/wireguard v0.0.0-20230325221338-052af4a8072b h1:J1CaxgLerRR5lgx3wnr6L04cJFbWoceSK9JWBdglINo=
 golang.zx2c4.com/wireguard v0.0.0-20230325221338-052af4a8072b/go.mod h1:tqur9LnfstdR9ep2LaJT4lFUl0EjlHtge+gAjmsHUG4=
 golang.zx2c4.com/wireguard/wgctrl v0.0.0-20230429144221-925a1e7659e6 h1:CawjfCvYQH2OU3/TnxLx97WDSUDRABfT18pCOYwc2GE=
 golang.zx2c4.com/wireguard/wgctrl v0.0.0-20230429144221-925a1e7659e6/go.mod h1:3rxYc4HtVcSG9gVaTs2GEBdehh+sYPOwKtyUWEOTb80=
+gonum.org/v1/gonum v0.16.0 h1:5+ul4Swaf3ESvrOnidPp4GZbzf0mxVQpDCYUQE7OJfk=
+gonum.org/v1/gonum v0.16.0/go.mod h1:fef3am4MQ93R2HHpKnLk4/Tbh/s0+wqD5nfa6Pnwy4E=
+google.golang.org/genproto/googleapis/api v0.0.0-20260209200024-4cfbd4190f57 h1:JLQynH/LBHfCTSbDWl+py8C+Rg/k1OVH3xfcaiANuF0=
+google.golang.org/genproto/googleapis/api v0.0.0-20260209200024-4cfbd4190f57/go.mod h1:kSJwQxqmFXeo79zOmbrALdflXQeAYcUbgS7PbpMknCY=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20260209200024-4cfbd4190f57 h1:mWPCjDEyshlQYzBpMNHaEof6UX1PmHcaUODUywQ0uac=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20260209200024-4cfbd4190f57/go.mod h1:j9x/tPzZkyxcgEFkiKEEGxfvyumM01BEtsW8xzOahRQ=
+google.golang.org/grpc v1.79.3 h1:sybAEdRIEtvcD68Gx7dmnwjZKlyfuc61Dyo9pGXXkKE=
+google.golang.org/grpc v1.79.3/go.mod h1:KmT0Kjez+0dde/v2j9vzwoAScgEPx/Bw1CYChhHLrHQ=
+google.golang.org/protobuf v1.36.11 h1:fV6ZwhNocDyBLK0dj+fg8ektcVegBBuEolpbTQyBNVE=
+google.golang.org/protobuf v1.36.11/go.mod h1:HTf+CrKn2C3g5S8VImy6tdcUvCska2kB7j23XfzDpco=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

internal/metrics/metrics.go

@@ -0,0 +1,506 @@
+// Package metrics provides the application-level metrics facade for Gerbil.
+//
+// Application code (main, relay, proxy) uses only the Record* functions in this
+// package. The actual recording is delegated to the backend selected in
+// internal/observability. Neither Prometheus nor OTel packages are imported here.
+package metrics
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/fosrl/gerbil/internal/observability"
+)
+
+// Config is the metrics configuration type. It is an alias for
+// observability.MetricsConfig so callers do not need to import observability.
+type Config = observability.MetricsConfig
+
+// PrometheusConfig is re-exported for convenience.
+type PrometheusConfig = observability.PrometheusConfig
+
+// OTelConfig is re-exported for convenience.
+type OTelConfig = observability.OTelConfig
+
+var (
+	backend observability.Backend
+
+	// Interface and peer metrics
+	wgInterfaceUp      observability.Int64Gauge
+	wgPeersTotal       observability.UpDownCounter
+	wgPeerConnected    observability.Int64Gauge
+	wgHandshakesTotal  observability.Counter
+	wgHandshakeLatency observability.Histogram
+	wgPeerRTT          observability.Histogram
+	wgBytesReceived    observability.Counter
+	wgBytesTransmitted observability.Counter
+	allowedIPsCount    observability.UpDownCounter
+	keyRotationTotal   observability.Counter
+
+	// System and proxy metrics
+	netlinkEventsTotal     observability.Counter
+	netlinkErrorsTotal     observability.Counter
+	syncDuration           observability.Histogram
+	workqueueDepth         observability.UpDownCounter
+	kernelModuleLoads      observability.Counter
+	firewallRulesApplied   observability.Counter
+	activeSessions         observability.UpDownCounter
+	activeProxyConnections observability.UpDownCounter
+	proxyRouteLookups      observability.Counter
+	proxyTLSHandshake      observability.Histogram
+	proxyBytesTransmitted  observability.Counter
+
+	// UDP Relay / Proxy Metrics
+	udpPacketsTotal            observability.Counter
+	udpPacketSizeBytes         observability.Histogram
+	holePunchEventsTotal       observability.Counter
+	proxyMappingActive         observability.UpDownCounter
+	sessionActive              observability.UpDownCounter
+	sessionRebuiltTotal        observability.Counter
+	commPatternActive          observability.UpDownCounter
+	proxyCleanupRemovedTotal   observability.Counter
+	proxyConnectionErrorsTotal observability.Counter
+	proxyInitialMappingsTotal  observability.Int64Gauge
+	proxyMappingUpdatesTotal   observability.Counter
+	proxyIdleCleanupDuration   observability.Histogram
+
+	// SNI Proxy Metrics
+	sniConnectionsTotal              observability.Counter
+	sniConnectionDuration            observability.Histogram
+	sniActiveConnections             observability.UpDownCounter
+	sniRouteCacheHitsTotal           observability.Counter
+	sniRouteAPIRequestsTotal         observability.Counter
+	sniRouteAPILatency               observability.Histogram
+	sniLocalOverrideTotal            observability.Counter
+	sniTrustedProxyEventsTotal       observability.Counter
+	sniProxyProtocolParseErrorsTotal observability.Counter
+	sniDataBytesTotal                observability.Counter
+	sniTunnelTerminationsTotal       observability.Counter
+
+	// HTTP API & Peer Management Metrics
+	httpRequestsTotal               observability.Counter
+	httpRequestDuration             observability.Histogram
+	peerOperationsTotal             observability.Counter
+	proxyMappingUpdateRequestsTotal observability.Counter
+	destinationsUpdateRequestsTotal observability.Counter
+
+	// Remote Configuration, Reporting & Housekeeping
+	remoteConfigFetchesTotal observability.Counter
+	bandwidthReportsTotal    observability.Counter
+	peerBandwidthBytesTotal  observability.Counter
+	memorySpikeTotal         observability.Counter
+	heapProfilesWrittenTotal observability.Counter
+
+	// Operational metrics
+	configReloadsTotal    observability.Counter
+	restartTotal          observability.Counter
+	authFailuresTotal     observability.Counter
+	aclDeniedTotal        observability.Counter
+	certificateExpiryDays observability.Float64Gauge
+)
+
+// DefaultConfig returns a default metrics configuration.
+func DefaultConfig() Config {
+	return observability.DefaultMetricsConfig()
+}
+
+// Initialize sets up the metrics system using the selected backend.
+// It returns the /metrics HTTP handler (non-nil only for Prometheus backend).
+func Initialize(cfg Config) (http.Handler, error) {
+	b, err := observability.New(cfg)
+	if err != nil {
+		return nil, err
+	}
+	backend = b
+
+	if err := createInstruments(); err != nil {
+		return nil, err
+	}
+
+	return backend.HTTPHandler(), nil
+}
+
+// Shutdown gracefully shuts down the metrics backend.
+func Shutdown(ctx context.Context) error {
+	if backend != nil {
+		return backend.Shutdown(ctx)
+	}
+	return nil
+}
+
+func createInstruments() error {
+	durationBuckets := []float64{0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10, 30}
+	sizeBuckets := []float64{512, 1024, 4096, 16384, 65536, 262144, 1048576}
+	sniDurationBuckets := []float64{0.1, 0.5, 1, 2.5, 5, 10, 30, 60, 120}
+
+	b := backend
+
+	wgInterfaceUp = b.NewInt64Gauge("gerbil_wg_interface_up",
+		"Operational state of a WireGuard interface (1=up, 0=down)", "ifname", "instance")
+	wgPeersTotal = b.NewUpDownCounter("gerbil_wg_peers_total",
+		"Total number of configured peers per interface", "ifname")
+	wgPeerConnected = b.NewInt64Gauge("gerbil_wg_peer_connected",
+		"Whether a specific peer is connected (1=connected, 0=disconnected)", "ifname", "peer")
+	allowedIPsCount = b.NewUpDownCounter("gerbil_allowed_ips_count",
+		"Number of allowed IPs configured per peer", "ifname", "peer")
+	keyRotationTotal = b.NewCounter("gerbil_key_rotation_total",
+		"Key rotation events", "ifname", "reason")
+	wgHandshakesTotal = b.NewCounter("gerbil_wg_handshakes_total",
+		"Count of handshake attempts with their result status", "ifname", "peer", "result")
+	wgHandshakeLatency = b.NewHistogram("gerbil_wg_handshake_latency_seconds",
+		"Distribution of handshake latencies in seconds", durationBuckets, "ifname", "peer")
+	wgPeerRTT = b.NewHistogram("gerbil_wg_peer_rtt_seconds",
+		"Observed round-trip time to a peer in seconds", durationBuckets, "ifname", "peer")
+	wgBytesReceived = b.NewCounter("gerbil_wg_bytes_received_total",
+		"Number of bytes received from a peer", "ifname", "peer")
+	wgBytesTransmitted = b.NewCounter("gerbil_wg_bytes_transmitted_total",
+		"Number of bytes transmitted to a peer", "ifname", "peer")
+	netlinkEventsTotal = b.NewCounter("gerbil_netlink_events_total",
+		"Number of netlink events processed", "event_type")
+	netlinkErrorsTotal = b.NewCounter("gerbil_netlink_errors_total",
+		"Count of netlink or kernel errors", "component", "error_type")
+	syncDuration = b.NewHistogram("gerbil_sync_duration_seconds",
+		"Duration of reconciliation/sync loops in seconds", durationBuckets, "component")
+	workqueueDepth = b.NewUpDownCounter("gerbil_workqueue_depth",
+		"Current length of internal work queues", "queue")
+	kernelModuleLoads = b.NewCounter("gerbil_kernel_module_loads_total",
+		"Count of kernel module load attempts", "result")
+	firewallRulesApplied = b.NewCounter("gerbil_firewall_rules_applied_total",
+		"IPTables/NFT rules applied", "result", "chain")
+	activeSessions = b.NewUpDownCounter("gerbil_active_sessions",
+		"Number of active UDP relay sessions", "ifname")
+	activeProxyConnections = b.NewUpDownCounter("gerbil_active_proxy_connections",
+		"Active SNI proxy connections")
+	proxyRouteLookups = b.NewCounter("gerbil_proxy_route_lookups_total",
+		"Number of route lookups", "result")
+	proxyTLSHandshake = b.NewHistogram("gerbil_proxy_tls_handshake_seconds",
+		"TLS handshake duration for SNI proxy in seconds", durationBuckets)
+	proxyBytesTransmitted = b.NewCounter("gerbil_proxy_bytes_transmitted_total",
+		"Bytes sent/received by the SNI proxy", "direction")
+	configReloadsTotal = b.NewCounter("gerbil_config_reloads_total",
+		"Number of configuration reloads", "result")
+	restartTotal = b.NewCounter("gerbil_restart_total",
+		"Process restart count")
+	authFailuresTotal = b.NewCounter("gerbil_auth_failures_total",
+		"Count of authentication or peer validation failures", "peer", "reason")
+	aclDeniedTotal = b.NewCounter("gerbil_acl_denied_total",
+		"Access control denied events", "ifname", "peer", "policy")
+	certificateExpiryDays = b.NewFloat64Gauge("gerbil_certificate_expiry_days",
+		"Days until certificate expiry", "cert_name", "ifname")
+	udpPacketsTotal = b.NewCounter("gerbil_udp_packets_total",
+		"Count of UDP packets processed by relay workers", "ifname", "type", "direction")
+	udpPacketSizeBytes = b.NewHistogram("gerbil_udp_packet_size_bytes",
+		"Size distribution of packets forwarded through relay", sizeBuckets, "ifname", "type")
+	holePunchEventsTotal = b.NewCounter("gerbil_hole_punch_events_total",
+		"Count of hole punch messages processed", "ifname", "result")
+	proxyMappingActive = b.NewUpDownCounter("gerbil_proxy_mapping_active",
+		"Number of active proxy mappings", "ifname")
+	sessionActive = b.NewUpDownCounter("gerbil_session_active",
+		"Number of active WireGuard sessions", "ifname")
+	sessionRebuiltTotal = b.NewCounter("gerbil_session_rebuilt_total",
+		"Count of sessions rebuilt from communication patterns", "ifname")
+	commPatternActive = b.NewUpDownCounter("gerbil_comm_pattern_active",
+		"Number of active communication patterns", "ifname")
+	proxyCleanupRemovedTotal = b.NewCounter("gerbil_proxy_cleanup_removed_total",
+		"Count of items removed during cleanup routines", "ifname", "component")
+	proxyConnectionErrorsTotal = b.NewCounter("gerbil_proxy_connection_errors_total",
+		"Count of connection errors in proxy operations", "ifname", "error_type")
+	proxyInitialMappingsTotal = b.NewInt64Gauge("gerbil_proxy_initial_mappings",
+		"Number of initial proxy mappings loaded", "ifname")
+	proxyMappingUpdatesTotal = b.NewCounter("gerbil_proxy_mapping_updates_total",
+		"Count of proxy mapping updates", "ifname")
+	proxyIdleCleanupDuration = b.NewHistogram("gerbil_proxy_idle_cleanup_duration_seconds",
+		"Duration of cleanup cycles", durationBuckets, "ifname", "component")
+	sniConnectionsTotal = b.NewCounter("gerbil_sni_connections_total",
+		"Count of connections processed by SNI proxy", "result")
+	sniConnectionDuration = b.NewHistogram("gerbil_sni_connection_duration_seconds",
+		"Lifetime distribution of proxied TLS connections", sniDurationBuckets)
+	sniActiveConnections = b.NewUpDownCounter("gerbil_sni_active_connections",
+		"Number of active SNI tunnels")
+	sniRouteCacheHitsTotal = b.NewCounter("gerbil_sni_route_cache_hits_total",
+		"Count of route cache hits and misses", "result")
+	sniRouteAPIRequestsTotal = b.NewCounter("gerbil_sni_route_api_requests_total",
+		"Count of route API requests", "result")
+	sniRouteAPILatency = b.NewHistogram("gerbil_sni_route_api_latency_seconds",
+		"Distribution of route API call latencies", durationBuckets)
+	sniLocalOverrideTotal = b.NewCounter("gerbil_sni_local_override_total",
+		"Count of routes using local overrides", "hit")
+	sniTrustedProxyEventsTotal = b.NewCounter("gerbil_sni_trusted_proxy_events_total",
+		"Count of PROXY protocol events", "event")
+	sniProxyProtocolParseErrorsTotal = b.NewCounter("gerbil_sni_proxy_protocol_parse_errors_total",
+		"Count of PROXY protocol parse failures")
+	sniDataBytesTotal = b.NewCounter("gerbil_sni_data_bytes_total",
+		"Count of bytes proxied through SNI tunnels", "direction")
+	sniTunnelTerminationsTotal = b.NewCounter("gerbil_sni_tunnel_terminations_total",
+		"Count of tunnel terminations by reason", "reason")
+	httpRequestsTotal = b.NewCounter("gerbil_http_requests_total",
+		"Count of HTTP requests to management API", "endpoint", "method", "status_code")
+	httpRequestDuration = b.NewHistogram("gerbil_http_request_duration_seconds",
+		"Distribution of HTTP request handling time", durationBuckets, "endpoint", "method")
+	peerOperationsTotal = b.NewCounter("gerbil_peer_operations_total",
+		"Count of peer lifecycle operations", "operation", "result")
+	proxyMappingUpdateRequestsTotal = b.NewCounter("gerbil_proxy_mapping_update_requests_total",
+		"Count of proxy mapping update API calls", "result")
+	destinationsUpdateRequestsTotal = b.NewCounter("gerbil_destinations_update_requests_total",
+		"Count of destinations update API calls", "result")
+	remoteConfigFetchesTotal = b.NewCounter("gerbil_remote_config_fetches_total",
+		"Count of remote configuration fetch attempts", "result")
+	bandwidthReportsTotal = b.NewCounter("gerbil_bandwidth_reports_total",
+		"Count of bandwidth report transmissions", "result")
+	peerBandwidthBytesTotal = b.NewCounter("gerbil_peer_bandwidth_bytes_total",
+		"Bytes per peer tracked by bandwidth calculation", "peer", "direction")
+	memorySpikeTotal = b.NewCounter("gerbil_memory_spike_total",
+		"Count of memory spikes detected", "severity")
+	heapProfilesWrittenTotal = b.NewCounter("gerbil_heap_profiles_written_total",
+		"Count of heap profile files generated")
+
+	return nil
+}
+
+func RecordInterfaceUp(ifname, instance string, up bool) {
+	value := int64(0)
+	if up {
+		value = 1
+	}
+	wgInterfaceUp.Record(context.Background(), value, observability.Labels{"ifname": ifname, "instance": instance})
+}
+
+func RecordPeersTotal(ifname string, delta int64) {
+	wgPeersTotal.Add(context.Background(), delta, observability.Labels{"ifname": ifname})
+}
+
+func RecordPeerConnected(ifname, peer string, connected bool) {
+	value := int64(0)
+	if connected {
+		value = 1
+	}
+	wgPeerConnected.Record(context.Background(), value, observability.Labels{"ifname": ifname, "peer": peer})
+}
+
+func RecordHandshake(ifname, peer, result string) {
+	wgHandshakesTotal.Add(context.Background(), 1, observability.Labels{"ifname": ifname, "peer": peer, "result": result})
+}
+
+func RecordHandshakeLatency(ifname, peer string, seconds float64) {
+	wgHandshakeLatency.Record(context.Background(), seconds, observability.Labels{"ifname": ifname, "peer": peer})
+}
+
+func RecordPeerRTT(ifname, peer string, seconds float64) {
+	wgPeerRTT.Record(context.Background(), seconds, observability.Labels{"ifname": ifname, "peer": peer})
+}
+
+func RecordBytesReceived(ifname, peer string, bytes int64) {
+	wgBytesReceived.Add(context.Background(), bytes, observability.Labels{"ifname": ifname, "peer": peer})
+}
+
+func RecordBytesTransmitted(ifname, peer string, bytes int64) {
+	wgBytesTransmitted.Add(context.Background(), bytes, observability.Labels{"ifname": ifname, "peer": peer})
+}
+
+func RecordAllowedIPsCount(ifname, peer string, delta int64) {
+	allowedIPsCount.Add(context.Background(), delta, observability.Labels{"ifname": ifname, "peer": peer})
+}
+
+func RecordKeyRotation(ifname, reason string) {
+	keyRotationTotal.Add(context.Background(), 1, observability.Labels{"ifname": ifname, "reason": reason})
+}
+
+func RecordNetlinkEvent(eventType string) {
+	netlinkEventsTotal.Add(context.Background(), 1, observability.Labels{"event_type": eventType})
+}
+
+func RecordNetlinkError(component, errorType string) {
+	netlinkErrorsTotal.Add(context.Background(), 1, observability.Labels{"component": component, "error_type": errorType})
+}
+
+func RecordSyncDuration(component string, seconds float64) {
+	syncDuration.Record(context.Background(), seconds, observability.Labels{"component": component})
+}
+
+func RecordWorkqueueDepth(queue string, delta int64) {
+	workqueueDepth.Add(context.Background(), delta, observability.Labels{"queue": queue})
+}
+
+func RecordKernelModuleLoad(result string) {
+	kernelModuleLoads.Add(context.Background(), 1, observability.Labels{"result": result})
+}
+
+func RecordFirewallRuleApplied(result, chain string) {
+	firewallRulesApplied.Add(context.Background(), 1, observability.Labels{"result": result, "chain": chain})
+}
+
+func RecordActiveSession(ifname string, delta int64) {
+	activeSessions.Add(context.Background(), delta, observability.Labels{"ifname": ifname})
+}
+
+func RecordActiveProxyConnection(hostname string, delta int64) {
+	_ = hostname
+	activeProxyConnections.Add(context.Background(), delta, nil)
+}
+
+func RecordProxyRouteLookup(result, hostname string) {
+	_ = hostname
+	proxyRouteLookups.Add(context.Background(), 1, observability.Labels{"result": result})
+}
+
+func RecordProxyTLSHandshake(hostname string, seconds float64) {
+	_ = hostname
+	proxyTLSHandshake.Record(context.Background(), seconds, nil)
+}
+
+func RecordProxyBytesTransmitted(hostname, direction string, bytes int64) {
+	_ = hostname
+	proxyBytesTransmitted.Add(context.Background(), bytes, observability.Labels{"direction": direction})
+}
+
+func RecordConfigReload(result string) {
+	configReloadsTotal.Add(context.Background(), 1, observability.Labels{"result": result})
+}
+
+func RecordRestart() {
+	restartTotal.Add(context.Background(), 1, nil)
+}
+
+func RecordAuthFailure(peer, reason string) {
+	authFailuresTotal.Add(context.Background(), 1, observability.Labels{"peer": peer, "reason": reason})
+}
+
+func RecordACLDenied(ifname, peer, policy string) {
+	aclDeniedTotal.Add(context.Background(), 1, observability.Labels{"ifname": ifname, "peer": peer, "policy": policy})
+}
+
+func RecordCertificateExpiry(certName, ifname string, days float64) {
+	certificateExpiryDays.Record(context.Background(), days, observability.Labels{"cert_name": certName, "ifname": ifname})
+}
+
+func RecordUDPPacket(ifname, packetType, direction string) {
+	udpPacketsTotal.Add(context.Background(), 1, observability.Labels{"ifname": ifname, "type": packetType, "direction": direction})
+}
+
+func RecordUDPPacketSize(ifname, packetType string, bytes float64) {
+	udpPacketSizeBytes.Record(context.Background(), bytes, observability.Labels{"ifname": ifname, "type": packetType})
+}
+
+func RecordHolePunchEvent(ifname, result string) {
+	holePunchEventsTotal.Add(context.Background(), 1, observability.Labels{"ifname": ifname, "result": result})
+}
+
+func RecordProxyMapping(ifname string, delta int64) {
+	proxyMappingActive.Add(context.Background(), delta, observability.Labels{"ifname": ifname})
+}
+
+func RecordSession(ifname string, delta int64) {
+	sessionActive.Add(context.Background(), delta, observability.Labels{"ifname": ifname})
+}
+
+func RecordSessionRebuilt(ifname string) {
+	sessionRebuiltTotal.Add(context.Background(), 1, observability.Labels{"ifname": ifname})
+}
+
+func RecordCommPattern(ifname string, delta int64) {
+	commPatternActive.Add(context.Background(), delta, observability.Labels{"ifname": ifname})
+}
+
+func RecordProxyCleanupRemoved(ifname, component string, count int64) {
+	proxyCleanupRemovedTotal.Add(context.Background(), count, observability.Labels{"ifname": ifname, "component": component})
+}
+
+func RecordProxyConnectionError(ifname, errorType string) {
+	proxyConnectionErrorsTotal.Add(context.Background(), 1, observability.Labels{"ifname": ifname, "error_type": errorType})
+}
+
+func RecordProxyInitialMappings(ifname string, count int64) {
+	proxyInitialMappingsTotal.Record(context.Background(), count, observability.Labels{"ifname": ifname})
+}
+
+func RecordProxyMappingUpdate(ifname string) {
+	proxyMappingUpdatesTotal.Add(context.Background(), 1, observability.Labels{"ifname": ifname})
+}
+
+func RecordProxyIdleCleanupDuration(ifname, component string, seconds float64) {
+	proxyIdleCleanupDuration.Record(context.Background(), seconds, observability.Labels{"ifname": ifname, "component": component})
+}
+
+func RecordSNIConnection(result string) {
+	sniConnectionsTotal.Add(context.Background(), 1, observability.Labels{"result": result})
+}
+
+func RecordSNIConnectionDuration(seconds float64) {
+	sniConnectionDuration.Record(context.Background(), seconds, nil)
+}
+
+func RecordSNIActiveConnection(delta int64) {
+	sniActiveConnections.Add(context.Background(), delta, nil)
+}
+
+func RecordSNIRouteCacheHit(result string) {
+	sniRouteCacheHitsTotal.Add(context.Background(), 1, observability.Labels{"result": result})
+}
+
+func RecordSNIRouteAPIRequest(result string) {
+	sniRouteAPIRequestsTotal.Add(context.Background(), 1, observability.Labels{"result": result})
+}
+
+func RecordSNIRouteAPILatency(seconds float64) {
+	sniRouteAPILatency.Record(context.Background(), seconds, nil)
+}
+
+func RecordSNILocalOverride(hit string) {
+	sniLocalOverrideTotal.Add(context.Background(), 1, observability.Labels{"hit": hit})
+}
+
+func RecordSNITrustedProxyEvent(event string) {
+	sniTrustedProxyEventsTotal.Add(context.Background(), 1, observability.Labels{"event": event})
+}
+
+func RecordSNIProxyProtocolParseError() {
+	sniProxyProtocolParseErrorsTotal.Add(context.Background(), 1, nil)
+}
+
+func RecordSNIDataBytes(direction string, bytes int64) {
+	sniDataBytesTotal.Add(context.Background(), bytes, observability.Labels{"direction": direction})
+}
+
+func RecordSNITunnelTermination(reason string) {
+	sniTunnelTerminationsTotal.Add(context.Background(), 1, observability.Labels{"reason": reason})
+}
+
+func RecordHTTPRequest(endpoint, method, statusCode string) {
+	httpRequestsTotal.Add(context.Background(), 1, observability.Labels{"endpoint": endpoint, "method": method, "status_code": statusCode})
+}
+
+func RecordHTTPRequestDuration(endpoint, method string, seconds float64) {
+	httpRequestDuration.Record(context.Background(), seconds, observability.Labels{"endpoint": endpoint, "method": method})
+}
+
+func RecordPeerOperation(operation, result string) {
+	peerOperationsTotal.Add(context.Background(), 1, observability.Labels{"operation": operation, "result": result})
+}
+
+func RecordProxyMappingUpdateRequest(result string) {
+	proxyMappingUpdateRequestsTotal.Add(context.Background(), 1, observability.Labels{"result": result})
+}
+
+func RecordDestinationsUpdateRequest(result string) {
+	destinationsUpdateRequestsTotal.Add(context.Background(), 1, observability.Labels{"result": result})
+}
+
+func RecordRemoteConfigFetch(result string) {
+	remoteConfigFetchesTotal.Add(context.Background(), 1, observability.Labels{"result": result})
+}
+
+func RecordBandwidthReport(result string) {
+	bandwidthReportsTotal.Add(context.Background(), 1, observability.Labels{"result": result})
+}
+
+func RecordPeerBandwidthBytes(peer, direction string, bytes int64) {
+	peerBandwidthBytesTotal.Add(context.Background(), bytes, observability.Labels{"peer": peer, "direction": direction})
+}
+
+func RecordMemorySpike(severity string) {
+	memorySpikeTotal.Add(context.Background(), 1, observability.Labels{"severity": severity})
+}
+
+func RecordHeapProfileWritten() {
+	heapProfilesWrittenTotal.Add(context.Background(), 1, nil)
+}

internal/metrics/metrics_test.go

@@ -0,0 +1,258 @@
+package metrics_test
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/fosrl/gerbil/internal/metrics"
+	"github.com/fosrl/gerbil/internal/observability"
+)
+
+const exampleHostname = "example.com"
+
+func initPrometheus(t *testing.T) http.Handler {
+	t.Helper()
+	cfg := metrics.DefaultConfig()
+	cfg.Enabled = true
+	cfg.Backend = "prometheus"
+	cfg.Prometheus.Path = "/metrics"
+
+	h, err := metrics.Initialize(cfg)
+	if err != nil {
+		t.Fatalf("Initialize failed: %v", err)
+	}
+	t.Cleanup(func() {
+		metrics.Shutdown(context.Background()) //nolint:errcheck
+	})
+	return h
+}
+
+func initNoop(t *testing.T) {
+	t.Helper()
+	cfg := metrics.DefaultConfig()
+	cfg.Enabled = false
+	_, err := metrics.Initialize(cfg)
+	if err != nil {
+		t.Fatalf("Initialize noop failed: %v", err)
+	}
+	t.Cleanup(func() {
+		metrics.Shutdown(context.Background()) //nolint:errcheck
+	})
+}
+
+func scrape(t *testing.T, h http.Handler) string {
+	t.Helper()
+	req := httptest.NewRequest(http.MethodGet, "/metrics", http.NoBody)
+	rr := httptest.NewRecorder()
+	h.ServeHTTP(rr, req)
+	if rr.Code != http.StatusOK {
+		t.Fatalf("scrape returned %d", rr.Code)
+	}
+	b, _ := io.ReadAll(rr.Body)
+	return string(b)
+}
+
+func assertContains(t *testing.T, body, substr string) {
+	t.Helper()
+	if !strings.Contains(body, substr) {
+		t.Errorf("expected %q in output\nbody:\n%s", substr, body)
+	}
+}
+
+// --- Tests ---
+
+func TestInitializePrometheus(t *testing.T) {
+	h := initPrometheus(t)
+	if h == nil {
+		t.Error("expected non-nil HTTP handler for prometheus backend")
+	}
+}
+
+func TestInitializeNoop(t *testing.T) {
+	initNoop(t)
+	// All Record* functions must not panic when noop backend is active.
+	metrics.RecordRestart()
+	metrics.RecordHTTPRequest("/test", "GET", "200")
+	metrics.RecordSNIConnection("accepted")
+	metrics.RecordPeersTotal("wg0", 1)
+}
+
+func TestDefaultConfig(t *testing.T) {
+	cfg := metrics.DefaultConfig()
+	if cfg.Backend != "prometheus" {
+		t.Errorf("expected prometheus default backend, got %q", cfg.Backend)
+	}
+}
+
+func TestShutdownNoInit(t *testing.T) {
+	// Shutdown without Initialize should not panic or error.
+	if err := metrics.Shutdown(context.Background()); err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+}
+
+func TestRecordHTTPRequest(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordHTTPRequest("/peers", "POST", "201")
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_http_requests_total")
+}
+
+func TestRecordHTTPRequestDuration(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordHTTPRequestDuration("/peers", "POST", 0.05)
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_http_request_duration_seconds")
+}
+
+func TestRecordInterfaceUp(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordInterfaceUp("wg0", "host1", true)
+	metrics.RecordInterfaceUp("wg0", "host1", false)
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_wg_interface_up")
+}
+
+func TestRecordPeersTotal(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordPeersTotal("wg0", 3)
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_wg_peers_total")
+}
+
+func TestRecordBytesReceivedTransmitted(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordBytesReceived("wg0", "peer1", 1024)
+	metrics.RecordBytesTransmitted("wg0", "peer1", 512)
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_wg_bytes_received_total")
+	assertContains(t, body, "gerbil_wg_bytes_transmitted_total")
+}
+
+func TestRecordSNI(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordSNIConnection("accepted")
+	metrics.RecordSNIActiveConnection(1)
+	metrics.RecordSNIConnectionDuration(1.5)
+	metrics.RecordSNIRouteCacheHit("hit")
+	metrics.RecordSNIRouteAPIRequest("success")
+	metrics.RecordSNIRouteAPILatency(0.01)
+	metrics.RecordSNILocalOverride("yes")
+	metrics.RecordSNITrustedProxyEvent("proxy_protocol_parsed")
+	metrics.RecordSNIProxyProtocolParseError()
+	metrics.RecordSNIDataBytes("client_to_target", 2048)
+	metrics.RecordSNITunnelTermination("eof")
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_sni_connections_total")
+	assertContains(t, body, "gerbil_sni_active_connections")
+}
+
+func TestRecordRelay(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordUDPPacket("relay", "data", "in")
+	metrics.RecordUDPPacketSize("relay", "data", 256)
+	metrics.RecordHolePunchEvent("relay", "success")
+	metrics.RecordProxyMapping("relay", 1)
+	metrics.RecordSession("relay", 1)
+	metrics.RecordSessionRebuilt("relay")
+	metrics.RecordCommPattern("relay", 1)
+	metrics.RecordProxyCleanupRemoved("relay", "session", 2)
+	metrics.RecordProxyConnectionError("relay", "dial_udp")
+	metrics.RecordProxyInitialMappings("relay", 5)
+	metrics.RecordProxyMappingUpdate("relay")
+	metrics.RecordProxyIdleCleanupDuration("relay", "conn", 0.1)
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_udp_packets_total")
+	assertContains(t, body, "gerbil_proxy_mapping_active")
+}
+
+func TestRecordWireGuard(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordHandshake("wg0", "peer1", "success")
+	metrics.RecordHandshakeLatency("wg0", "peer1", 0.02)
+	metrics.RecordPeerRTT("wg0", "peer1", 0.005)
+	metrics.RecordPeerConnected("wg0", "peer1", true)
+	metrics.RecordAllowedIPsCount("wg0", "peer1", 2)
+	metrics.RecordKeyRotation("wg0", "scheduled")
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_wg_handshakes_total")
+	assertContains(t, body, "gerbil_wg_peer_connected")
+}
+
+func TestRecordHousekeeping(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordRemoteConfigFetch("success")
+	metrics.RecordBandwidthReport("success")
+	metrics.RecordPeerBandwidthBytes("peer1", "rx", 512)
+	metrics.RecordMemorySpike("warning")
+	metrics.RecordHeapProfileWritten()
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_remote_config_fetches_total")
+	assertContains(t, body, "gerbil_memory_spike_total")
+}
+
+func TestRecordOperational(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordConfigReload("success")
+	metrics.RecordRestart()
+	metrics.RecordAuthFailure("peer1", "bad_key")
+	metrics.RecordACLDenied("wg0", "peer1", "default-deny")
+	metrics.RecordCertificateExpiry(exampleHostname, "wg0", 90.0)
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_config_reloads_total")
+	assertContains(t, body, "gerbil_restart_total")
+}
+
+func TestRecordNetlink(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordNetlinkEvent("link_up")
+	metrics.RecordNetlinkError("wg", "timeout")
+	metrics.RecordSyncDuration("config", 0.1)
+	metrics.RecordWorkqueueDepth("main", 3)
+	metrics.RecordKernelModuleLoad("success")
+	metrics.RecordFirewallRuleApplied("success", "INPUT")
+	metrics.RecordActiveSession("wg0", 1)
+	metrics.RecordActiveProxyConnection(exampleHostname, 1)
+	metrics.RecordProxyRouteLookup("hit", exampleHostname)
+	metrics.RecordProxyTLSHandshake(exampleHostname, 0.05)
+	metrics.RecordProxyBytesTransmitted(exampleHostname, "tx", 1024)
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_netlink_events_total")
+	assertContains(t, body, "gerbil_active_sessions")
+}
+
+func TestRecordPeerOperation(t *testing.T) {
+	h := initPrometheus(t)
+	metrics.RecordPeerOperation("add", "success")
+	metrics.RecordProxyMappingUpdateRequest("success")
+	metrics.RecordDestinationsUpdateRequest("success")
+	body := scrape(t, h)
+	assertContains(t, body, "gerbil_peer_operations_total")
+}
+
+func TestInitializeInvalidBackend(t *testing.T) {
+	cfg := observability.MetricsConfig{Enabled: true, Backend: "invalid"}
+	_, err := metrics.Initialize(cfg)
+	if err == nil {
+		t.Error("expected error for invalid backend")
+	}
+}
+
+func TestInitializeBackendNone(t *testing.T) {
+	cfg := metrics.DefaultConfig()
+	cfg.Backend = "none"
+	h, err := metrics.Initialize(cfg)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if h != nil {
+		t.Error("none backend should return nil handler")
+	}
+	// All Record* calls should be noop
+	metrics.RecordRestart()
+	metrics.Shutdown(context.Background()) //nolint:errcheck
+}

internal/observability/config.go

@@ -0,0 +1,119 @@
+// Package observability provides a backend-neutral metrics abstraction for Gerbil.
+//
+// Exactly one metrics backend may be enabled at runtime:
+//   - "prometheus" – native Prometheus client; exposes /metrics (no OTel SDK required)
+//   - "otel"       – OpenTelemetry metrics pushed via OTLP (gRPC or HTTP)
+//   - "none"       – metrics disabled; a safe noop implementation is used
+//
+// Future OTel tracing and logging can be added to this package alongside the
+// existing otel sub-package without touching the Prometheus-native path.
+package observability
+
+import (
+	"fmt"
+	"time"
+)
+
+// MetricsConfig is the top-level metrics configuration.
+type MetricsConfig struct {
+	// Enabled controls whether any metrics backend is started.
+	// When false the noop backend is used regardless of Backend.
+	Enabled bool
+
+	// Backend selects the active backend: "prometheus", "otel", or "none".
+	Backend string
+
+	// Prometheus holds settings used only by the Prometheus-native backend.
+	Prometheus PrometheusConfig
+
+	// OTel holds settings used only by the OTel backend.
+	OTel OTelConfig
+
+	// ServiceName is propagated to OTel resource attributes.
+	ServiceName string
+
+	// ServiceVersion is propagated to OTel resource attributes.
+	ServiceVersion string
+
+	// DeploymentEnvironment is an optional OTel resource attribute.
+	DeploymentEnvironment string
+}
+
+// PrometheusConfig holds Prometheus-native backend settings.
+type PrometheusConfig struct {
+	// Path is the HTTP path to expose the /metrics endpoint.
+	// Defaults to "/metrics".
+	Path string
+}
+
+// OTelConfig holds OpenTelemetry backend settings.
+type OTelConfig struct {
+	// Protocol is the OTLP transport: "grpc" (default) or "http".
+	Protocol string
+
+	// Endpoint is the OTLP collector address (e.g. "localhost:4317").
+	Endpoint string
+
+	// Insecure disables TLS for the OTLP connection.
+	Insecure bool
+
+	// ExportInterval is how often metrics are pushed to the collector.
+	// Defaults to 60 s.
+	ExportInterval time.Duration
+}
+
+// DefaultMetricsConfig returns a MetricsConfig with sensible defaults.
+func DefaultMetricsConfig() MetricsConfig {
+	return MetricsConfig{
+		Enabled: true,
+		Backend: "prometheus",
+		Prometheus: PrometheusConfig{
+			Path: "/metrics",
+		},
+		OTel: OTelConfig{
+			Protocol:       "grpc",
+			Endpoint:       "localhost:4317",
+			Insecure:       true,
+			ExportInterval: 60 * time.Second,
+		},
+		ServiceName:    "gerbil",
+		ServiceVersion: "1.0.0",
+	}
+}
+
+// Validate checks the configuration for logical errors.
+func (c *MetricsConfig) Validate() error {
+	if !c.Enabled {
+		return nil
+	}
+
+	switch c.Backend {
+	case "prometheus", "none", "":
+		// valid
+	case "otel":
+		if c.OTel.Endpoint == "" {
+			return fmt.Errorf("metrics: backend=otel requires a non-empty OTel endpoint")
+		}
+		if c.OTel.Protocol != "grpc" && c.OTel.Protocol != "http" {
+			return fmt.Errorf("metrics: otel protocol must be \"grpc\" or \"http\", got %q", c.OTel.Protocol)
+		}
+		if c.OTel.ExportInterval <= 0 {
+			return fmt.Errorf("metrics: otel export interval must be positive")
+		}
+	default:
+		return fmt.Errorf("metrics: unknown backend %q (must be \"prometheus\", \"otel\", or \"none\")", c.Backend)
+	}
+
+	return nil
+}
+
+// effectiveBackend resolves the backend string, treating "" and "none" as noop.
+func (c *MetricsConfig) effectiveBackend() string {
+	if !c.Enabled {
+		return "none"
+	}
+	if c.Backend == "" {
+		return "none"
+	}
+	return c.Backend
+}

internal/observability/metrics.go

@@ -0,0 +1,152 @@
+package observability
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	obsotel "github.com/fosrl/gerbil/internal/observability/otel"
+	obsprom "github.com/fosrl/gerbil/internal/observability/prometheus"
+)
+
+// Labels is a set of key-value pairs attached to a metric observation.
+// Use only stable, bounded-cardinality label values.
+type Labels = map[string]string
+
+// Counter is a monotonically increasing instrument.
+type Counter interface {
+	Add(ctx context.Context, value int64, labels Labels)
+}
+
+// UpDownCounter is a bidirectional integer instrument (can go up or down).
+type UpDownCounter interface {
+	Add(ctx context.Context, value int64, labels Labels)
+}
+
+// Int64Gauge records a snapshot integer value.
+type Int64Gauge interface {
+	Record(ctx context.Context, value int64, labels Labels)
+}
+
+// Float64Gauge records a snapshot float value.
+type Float64Gauge interface {
+	Record(ctx context.Context, value float64, labels Labels)
+}
+
+// Histogram records a distribution of values.
+type Histogram interface {
+	Record(ctx context.Context, value float64, labels Labels)
+}
+
+// Backend is the single interface that each metrics implementation must satisfy.
+// Application code must not import backend-specific packages (prometheus, otel).
+type Backend interface {
+	// NewCounter creates a counter metric.
+	// labelNames declares the set of label keys that will be passed at observation time.
+	NewCounter(name, desc string, labelNames ...string) Counter
+
+	// NewUpDownCounter creates an up-down counter metric.
+	NewUpDownCounter(name, desc string, labelNames ...string) UpDownCounter
+
+	// NewInt64Gauge creates an integer gauge metric.
+	NewInt64Gauge(name, desc string, labelNames ...string) Int64Gauge
+
+	// NewFloat64Gauge creates a float gauge metric.
+	NewFloat64Gauge(name, desc string, labelNames ...string) Float64Gauge
+
+	// NewHistogram creates a histogram metric.
+	// buckets are the explicit upper-bound bucket boundaries.
+	NewHistogram(name, desc string, buckets []float64, labelNames ...string) Histogram
+
+	// HTTPHandler returns the /metrics HTTP handler.
+	// Implementations that do not expose an HTTP endpoint return nil.
+	HTTPHandler() http.Handler
+
+	// Shutdown performs a graceful flush / shutdown of the backend.
+	Shutdown(ctx context.Context) error
+}
+
+// New creates the backend selected by cfg and returns it.
+// Exactly one backend is created; the selection is mutually exclusive.
+func New(cfg MetricsConfig) (Backend, error) {
+	if err := cfg.Validate(); err != nil {
+		return nil, err
+	}
+
+	switch cfg.effectiveBackend() {
+	case "prometheus":
+		b, err := obsprom.New(obsprom.Config{
+			Path: cfg.Prometheus.Path,
+		})
+		if err != nil {
+			return nil, err
+		}
+		return &promAdapter{b: b}, nil
+	case "otel":
+		b, err := obsotel.New(obsotel.Config{
+			Protocol:              cfg.OTel.Protocol,
+			Endpoint:              cfg.OTel.Endpoint,
+			Insecure:              cfg.OTel.Insecure,
+			ExportInterval:        cfg.OTel.ExportInterval,
+			ServiceName:           cfg.ServiceName,
+			ServiceVersion:        cfg.ServiceVersion,
+			DeploymentEnvironment: cfg.DeploymentEnvironment,
+		})
+		if err != nil {
+			return nil, err
+		}
+		return &otelAdapter{b: b}, nil
+	case "none":
+		return &NoopBackend{}, nil
+	default:
+		return nil, fmt.Errorf("observability: unknown backend %q", cfg.effectiveBackend())
+	}
+}
+
+// promAdapter wraps obsprom.Backend to implement the observability.Backend interface.
+// The concrete instrument types from the prometheus sub-package satisfy the instrument
+// interfaces via Go's structural (duck) typing without importing this package.
+type promAdapter struct {
+	b *obsprom.Backend
+}
+
+func (a *promAdapter) NewCounter(name, desc string, labelNames ...string) Counter {
+	return a.b.NewCounter(name, desc, labelNames...)
+}
+func (a *promAdapter) NewUpDownCounter(name, desc string, labelNames ...string) UpDownCounter {
+	return a.b.NewUpDownCounter(name, desc, labelNames...)
+}
+func (a *promAdapter) NewInt64Gauge(name, desc string, labelNames ...string) Int64Gauge {
+	return a.b.NewInt64Gauge(name, desc, labelNames...)
+}
+func (a *promAdapter) NewFloat64Gauge(name, desc string, labelNames ...string) Float64Gauge {
+	return a.b.NewFloat64Gauge(name, desc, labelNames...)
+}
+func (a *promAdapter) NewHistogram(name, desc string, buckets []float64, labelNames ...string) Histogram {
+	return a.b.NewHistogram(name, desc, buckets, labelNames...)
+}
+func (a *promAdapter) HTTPHandler() http.Handler          { return a.b.HTTPHandler() }
+func (a *promAdapter) Shutdown(ctx context.Context) error { return a.b.Shutdown(ctx) }
+
+// otelAdapter wraps obsotel.Backend to implement the observability.Backend interface.
+type otelAdapter struct {
+	b *obsotel.Backend
+}
+
+func (a *otelAdapter) NewCounter(name, desc string, labelNames ...string) Counter {
+	return a.b.NewCounter(name, desc, labelNames...)
+}
+func (a *otelAdapter) NewUpDownCounter(name, desc string, labelNames ...string) UpDownCounter {
+	return a.b.NewUpDownCounter(name, desc, labelNames...)
+}
+func (a *otelAdapter) NewInt64Gauge(name, desc string, labelNames ...string) Int64Gauge {
+	return a.b.NewInt64Gauge(name, desc, labelNames...)
+}
+func (a *otelAdapter) NewFloat64Gauge(name, desc string, labelNames ...string) Float64Gauge {
+	return a.b.NewFloat64Gauge(name, desc, labelNames...)
+}
+func (a *otelAdapter) NewHistogram(name, desc string, buckets []float64, labelNames ...string) Histogram {
+	return a.b.NewHistogram(name, desc, buckets, labelNames...)
+}
+func (a *otelAdapter) HTTPHandler() http.Handler          { return a.b.HTTPHandler() }
+func (a *otelAdapter) Shutdown(ctx context.Context) error { return a.b.Shutdown(ctx) }

internal/observability/metrics_test.go

@@ -0,0 +1,198 @@
+package observability_test
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/fosrl/gerbil/internal/observability"
+)
+
+const (
+	defaultMetricsPath = "/metrics"
+	otelGRPCEndpoint   = "localhost:4317"
+	errUnexpectedFmt   = "unexpected error: %v"
+)
+
+func TestDefaultMetricsConfig(t *testing.T) {
+	cfg := observability.DefaultMetricsConfig()
+	if !cfg.Enabled {
+		t.Error("default config should have Enabled=true")
+	}
+	if cfg.Backend != "prometheus" {
+		t.Errorf("default backend should be prometheus, got %q", cfg.Backend)
+	}
+	if cfg.Prometheus.Path != defaultMetricsPath {
+		t.Errorf("default prometheus path should be %s, got %q", defaultMetricsPath, cfg.Prometheus.Path)
+	}
+	if cfg.OTel.Protocol != "grpc" {
+		t.Errorf("default otel protocol should be grpc, got %q", cfg.OTel.Protocol)
+	}
+	if cfg.OTel.ExportInterval != 60*time.Second {
+		t.Errorf("default otel export interval should be 60s, got %v", cfg.OTel.ExportInterval)
+	}
+}
+func TestValidateValidConfigs(t *testing.T) {
+	tests := []struct {
+		name string
+		cfg  observability.MetricsConfig
+	}{
+		{name: "disabled", cfg: observability.MetricsConfig{Enabled: false}},
+		{name: "backend none", cfg: observability.MetricsConfig{Enabled: true, Backend: "none"}},
+		{name: "backend empty", cfg: observability.MetricsConfig{Enabled: true, Backend: ""}},
+		{name: "prometheus", cfg: observability.MetricsConfig{Enabled: true, Backend: "prometheus"}},
+		{
+			name: "otel grpc",
+			cfg: observability.MetricsConfig{
+				Enabled: true, Backend: "otel",
+				OTel: observability.OTelConfig{Protocol: "grpc", Endpoint: otelGRPCEndpoint, ExportInterval: 10 * time.Second},
+			},
+		},
+		{
+			name: "otel http",
+			cfg: observability.MetricsConfig{
+				Enabled: true, Backend: "otel",
+				OTel: observability.OTelConfig{Protocol: "http", Endpoint: "localhost:4318", ExportInterval: 30 * time.Second},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := tt.cfg.Validate(); err != nil {
+				t.Errorf("unexpected validation error: %v", err)
+			}
+		})
+	}
+}
+
+func TestValidateInvalidConfigs(t *testing.T) {
+	tests := []struct {
+		name string
+		cfg  observability.MetricsConfig
+	}{
+		{name: "unknown backend", cfg: observability.MetricsConfig{Enabled: true, Backend: "datadog"}},
+		{
+			name: "otel missing endpoint",
+			cfg: observability.MetricsConfig{
+				Enabled: true, Backend: "otel",
+				OTel: observability.OTelConfig{Protocol: "grpc", Endpoint: "", ExportInterval: 10 * time.Second},
+			},
+		},
+		{
+			name: "otel invalid protocol",
+			cfg: observability.MetricsConfig{
+				Enabled: true, Backend: "otel",
+				OTel: observability.OTelConfig{Protocol: "tcp", Endpoint: otelGRPCEndpoint, ExportInterval: 10 * time.Second},
+			},
+		},
+		{
+			name: "otel zero interval",
+			cfg: observability.MetricsConfig{
+				Enabled: true, Backend: "otel",
+				OTel: observability.OTelConfig{Protocol: "grpc", Endpoint: otelGRPCEndpoint, ExportInterval: 0},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := tt.cfg.Validate(); err == nil {
+				t.Error("expected validation error but got nil")
+			}
+		})
+	}
+}
+
+func TestNewNoopBackend(t *testing.T) {
+	b, err := observability.New(observability.MetricsConfig{Enabled: false})
+	if err != nil {
+		t.Fatalf(errUnexpectedFmt, err)
+	}
+	if b.HTTPHandler() != nil {
+		t.Error("noop backend HTTPHandler should return nil")
+	}
+}
+
+func TestNewNoneBackend(t *testing.T) {
+	b, err := observability.New(observability.MetricsConfig{Enabled: true, Backend: "none"})
+	if err != nil {
+		t.Fatalf(errUnexpectedFmt, err)
+	}
+	if b.HTTPHandler() != nil {
+		t.Error("none backend HTTPHandler should return nil")
+	}
+}
+
+func TestNewPrometheusBackend(t *testing.T) {
+	cfg := observability.MetricsConfig{
+		Enabled: true, Backend: "prometheus",
+		Prometheus: observability.PrometheusConfig{Path: defaultMetricsPath},
+	}
+	b, err := observability.New(cfg)
+	if err != nil {
+		t.Fatalf(errUnexpectedFmt, err)
+	}
+	if b.HTTPHandler() == nil {
+		t.Error("prometheus backend HTTPHandler should not be nil")
+	}
+	if err := b.Shutdown(context.Background()); err != nil {
+		t.Errorf("prometheus shutdown error: %v", err)
+	}
+}
+
+func TestNewInvalidBackend(t *testing.T) {
+	_, err := observability.New(observability.MetricsConfig{Enabled: true, Backend: "invalid"})
+	if err == nil {
+		t.Error("expected error for invalid backend")
+	}
+}
+
+func TestPrometheusAdapterAllInstruments(t *testing.T) {
+	b, err := observability.New(observability.MetricsConfig{
+		Enabled: true, Backend: "prometheus",
+		Prometheus: observability.PrometheusConfig{Path: defaultMetricsPath},
+	})
+	if err != nil {
+		t.Fatalf("failed to create backend: %v", err)
+	}
+	ctx := context.Background()
+	labels := observability.Labels{"k": "v"}
+
+	b.NewCounter("prom_adapter_counter_total", "desc", "k").Add(ctx, 1, labels)
+	b.NewUpDownCounter("prom_adapter_updown", "desc", "k").Add(ctx, 2, labels)
+	b.NewInt64Gauge("prom_adapter_int_gauge", "desc", "k").Record(ctx, 99, labels)
+	b.NewFloat64Gauge("prom_adapter_float_gauge", "desc", "k").Record(ctx, 1.23, labels)
+	b.NewHistogram("prom_adapter_histogram", "desc", []float64{0.1, 1.0}, "k").Record(ctx, 0.5, labels)
+
+	if b.HTTPHandler() == nil {
+		t.Error("prometheus adapter HTTPHandler should not be nil")
+	}
+	if err := b.Shutdown(ctx); err != nil {
+		t.Errorf("Shutdown error: %v", err)
+	}
+}
+
+func TestOtelAdapterAllInstruments(t *testing.T) {
+	b, err := observability.New(observability.MetricsConfig{
+		Enabled: true, Backend: "otel",
+		OTel: observability.OTelConfig{Protocol: "grpc", Endpoint: otelGRPCEndpoint, Insecure: true, ExportInterval: 100 * time.Millisecond},
+	})
+	if err != nil {
+		t.Fatalf("failed to create otel backend: %v", err)
+	}
+	ctx := context.Background()
+	labels := observability.Labels{"k": "v"}
+
+	b.NewCounter("otel_adapter_counter_total", "desc", "k").Add(ctx, 1, labels)
+	b.NewUpDownCounter("otel_adapter_updown", "desc", "k").Add(ctx, 2, labels)
+	b.NewInt64Gauge("otel_adapter_int_gauge", "desc", "k").Record(ctx, 99, labels)
+	b.NewFloat64Gauge("otel_adapter_float_gauge", "desc", "k").Record(ctx, 1.23, labels)
+	b.NewHistogram("otel_adapter_histogram", "desc", []float64{0.1, 1.0}, "k").Record(ctx, 0.5, labels)
+
+	if b.HTTPHandler() != nil {
+		t.Error("OTel adapter HTTPHandler should be nil")
+	}
+
+	shutdownCtx, cancel := context.WithTimeout(ctx, 2*time.Second)
+	defer cancel()
+	b.Shutdown(shutdownCtx) //nolint:errcheck
+}

internal/observability/noop.go

@@ -0,0 +1,71 @@
+package observability
+
+import (
+	"context"
+	"net/http"
+)
+
+// NoopBackend is a Backend that discards all observations.
+// It is used when metrics are disabled (Enabled=false or Backend="none").
+// All methods are safe to call concurrently.
+type NoopBackend struct{}
+
+// Compile-time interface check.
+var _ Backend = (*NoopBackend)(nil)
+
+func (n *NoopBackend) NewCounter(_ string, _ string, _ ...string) Counter {
+	_ = n
+	return noopCounter{}
+}
+
+func (n *NoopBackend) NewUpDownCounter(_ string, _ string, _ ...string) UpDownCounter {
+	_ = n
+	return noopUpDownCounter{}
+}
+
+func (n *NoopBackend) NewInt64Gauge(_ string, _ string, _ ...string) Int64Gauge {
+	_ = n
+	return noopInt64Gauge{}
+}
+
+func (n *NoopBackend) NewFloat64Gauge(_ string, _ string, _ ...string) Float64Gauge {
+	_ = n
+	return noopFloat64Gauge{}
+}
+
+func (n *NoopBackend) NewHistogram(_ string, _ string, _ []float64, _ ...string) Histogram {
+	_ = n
+	return noopHistogram{}
+}
+
+func (n *NoopBackend) HTTPHandler() http.Handler {
+	_ = n
+	return nil
+}
+
+func (n *NoopBackend) Shutdown(_ context.Context) error {
+	_ = n
+	return nil
+}
+
+// --- noop instrument types ---
+
+type noopCounter struct{}
+
+func (noopCounter) Add(_ context.Context, _ int64, _ Labels) { /* intentionally no-op */ }
+
+type noopUpDownCounter struct{}
+
+func (noopUpDownCounter) Add(_ context.Context, _ int64, _ Labels) { /* intentionally no-op */ }
+
+type noopInt64Gauge struct{}
+
+func (noopInt64Gauge) Record(_ context.Context, _ int64, _ Labels) { /* intentionally no-op */ }
+
+type noopFloat64Gauge struct{}
+
+func (noopFloat64Gauge) Record(_ context.Context, _ float64, _ Labels) { /* intentionally no-op */ }
+
+type noopHistogram struct{}
+
+func (noopHistogram) Record(_ context.Context, _ float64, _ Labels) { /* intentionally no-op */ }

internal/observability/noop_test.go

@@ -0,0 +1,67 @@
+package observability_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/fosrl/gerbil/internal/observability"
+)
+
+func TestNoopBackendAllInstruments(t *testing.T) {
+	n := &observability.NoopBackend{}
+
+	ctx := context.Background()
+	labels := observability.Labels{"k": "v"}
+
+	t.Run("Counter", func(_ *testing.T) {
+		c := n.NewCounter("test_counter", "desc")
+		c.Add(ctx, 1, labels)
+		c.Add(ctx, 0, nil)
+	})
+
+	t.Run("UpDownCounter", func(_ *testing.T) {
+		u := n.NewUpDownCounter("test_updown", "desc")
+		u.Add(ctx, 1, labels)
+		u.Add(ctx, -1, nil)
+	})
+
+	t.Run("Int64Gauge", func(_ *testing.T) {
+		g := n.NewInt64Gauge("test_int64gauge", "desc")
+		g.Record(ctx, 42, labels)
+		g.Record(ctx, 0, nil)
+	})
+
+	t.Run("Float64Gauge", func(_ *testing.T) {
+		g := n.NewFloat64Gauge("test_float64gauge", "desc")
+		g.Record(ctx, 3.14, labels)
+		g.Record(ctx, 0, nil)
+	})
+
+	t.Run("Histogram", func(_ *testing.T) {
+		h := n.NewHistogram("test_histogram", "desc", []float64{1, 5, 10})
+		h.Record(ctx, 2.5, labels)
+		h.Record(ctx, 0, nil)
+	})
+
+	t.Run("HTTPHandler", func(t *testing.T) {
+		if n.HTTPHandler() != nil {
+			t.Error("noop HTTPHandler should be nil")
+		}
+	})
+
+	t.Run("Shutdown", func(t *testing.T) {
+		if err := n.Shutdown(ctx); err != nil {
+			t.Errorf("noop Shutdown should not error: %v", err)
+		}
+	})
+}
+
+func TestNoopBackendLabelNames(_ *testing.T) {
+	// Verify that label names passed at creation time are accepted without panic.
+	n := &observability.NoopBackend{}
+	n.NewCounter("c", "d", "label1", "label2")
+	n.NewUpDownCounter("u", "d", "l1")
+	n.NewInt64Gauge("g1", "d", "l1", "l2", "l3")
+	n.NewFloat64Gauge("g2", "d")
+	n.NewHistogram("h", "d", []float64{0.1, 1.0}, "l1")
+}

internal/observability/otel/backend.go

@@ -0,0 +1,210 @@
+// Package otel implements the OpenTelemetry metrics backend for Gerbil.
+//
+// Metrics are exported via OTLP (gRPC or HTTP) to an external collector.
+// No Prometheus /metrics endpoint is exposed in this mode.
+// Future OTel tracing and logging can be added alongside this package
+// without touching the Prometheus-native path.
+package otel
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"time"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/metric"
+	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
+)
+
+// Config holds OTel backend configuration.
+type Config struct {
+	// Protocol is "grpc" (default) or "http".
+	Protocol string
+
+	// Endpoint is the OTLP collector address.
+	Endpoint string
+
+	// Insecure disables TLS.
+	Insecure bool
+
+	// ExportInterval is the period between pushes to the collector.
+	ExportInterval time.Duration
+
+	ServiceName           string
+	ServiceVersion        string
+	DeploymentEnvironment string
+}
+
+// Backend is the OTel metrics backend.
+type Backend struct {
+	cfg      Config
+	provider *sdkmetric.MeterProvider
+	meter    metric.Meter
+}
+
+// New creates and initialises an OTel backend.
+//
+// cfg.Protocol must be "grpc" (default) or "http".
+// cfg.Endpoint is the OTLP collector address (e.g. "localhost:4317").
+// cfg.ExportInterval sets the push period (defaults to 60 s if ≤ 0).
+// cfg.Insecure disables TLS on the OTLP connection.
+//
+// Connection to the collector is established lazily; New only validates cfg
+// and creates the SDK components. It returns an error only if the OTel resource
+// or exporter cannot be constructed.
+func New(cfg Config) (*Backend, error) {
+	if cfg.Protocol == "" {
+		cfg.Protocol = "grpc"
+	}
+	if cfg.ExportInterval <= 0 {
+		cfg.ExportInterval = 60 * time.Second
+	}
+	if cfg.ServiceName == "" {
+		cfg.ServiceName = "gerbil"
+	}
+
+	res, err := newResource(cfg.ServiceName, cfg.ServiceVersion, cfg.DeploymentEnvironment)
+	if err != nil {
+		return nil, fmt.Errorf("otel backend: build resource: %w", err)
+	}
+
+	exp, err := newExporter(context.Background(), cfg)
+	if err != nil {
+		return nil, fmt.Errorf("otel backend: create exporter: %w", err)
+	}
+
+	reader := sdkmetric.NewPeriodicReader(exp,
+		sdkmetric.WithInterval(cfg.ExportInterval),
+	)
+
+	provider := sdkmetric.NewMeterProvider(
+		sdkmetric.WithResource(res),
+		sdkmetric.WithReader(reader),
+	)
+
+	meter := provider.Meter("github.com/fosrl/gerbil")
+
+	return &Backend{cfg: cfg, provider: provider, meter: meter}, nil
+}
+
+// HTTPHandler returns nil – the OTel backend does not expose an HTTP endpoint.
+func (b *Backend) HTTPHandler() http.Handler {
+	_ = b
+	return nil
+}
+
+// Shutdown flushes pending metrics and shuts down the MeterProvider.
+func (b *Backend) Shutdown(ctx context.Context) error {
+	return b.provider.Shutdown(ctx)
+}
+
+// NewCounter creates an OTel Int64Counter.
+func (b *Backend) NewCounter(name, desc string, _ ...string) *Counter {
+	c, err := b.meter.Int64Counter(name, metric.WithDescription(desc))
+	if err != nil {
+		panic(fmt.Sprintf("otel: create counter %q: %v", name, err))
+	}
+	return &Counter{c: c}
+}
+
+// NewUpDownCounter creates an OTel Int64UpDownCounter.
+func (b *Backend) NewUpDownCounter(name, desc string, _ ...string) *UpDownCounter {
+	c, err := b.meter.Int64UpDownCounter(name, metric.WithDescription(desc))
+	if err != nil {
+		panic(fmt.Sprintf("otel: create up-down counter %q: %v", name, err))
+	}
+	return &UpDownCounter{c: c}
+}
+
+// NewInt64Gauge creates an OTel Int64Gauge.
+func (b *Backend) NewInt64Gauge(name, desc string, _ ...string) *Int64Gauge {
+	g, err := b.meter.Int64Gauge(name, metric.WithDescription(desc))
+	if err != nil {
+		panic(fmt.Sprintf("otel: create int64 gauge %q: %v", name, err))
+	}
+	return &Int64Gauge{g: g}
+}
+
+// NewFloat64Gauge creates an OTel Float64Gauge.
+func (b *Backend) NewFloat64Gauge(name, desc string, _ ...string) *Float64Gauge {
+	g, err := b.meter.Float64Gauge(name, metric.WithDescription(desc))
+	if err != nil {
+		panic(fmt.Sprintf("otel: create float64 gauge %q: %v", name, err))
+	}
+	return &Float64Gauge{g: g}
+}
+
+// NewHistogram creates an OTel Float64Histogram with explicit bucket boundaries.
+func (b *Backend) NewHistogram(name, desc string, buckets []float64, _ ...string) *Histogram {
+	h, err := b.meter.Float64Histogram(name,
+		metric.WithDescription(desc),
+		metric.WithExplicitBucketBoundaries(buckets...),
+	)
+	if err != nil {
+		panic(fmt.Sprintf("otel: create histogram %q: %v", name, err))
+	}
+	return &Histogram{h: h}
+}
+
+// labelsToAttrs converts a Labels map to OTel attribute key-value pairs.
+func labelsToAttrs(labels map[string]string) []attribute.KeyValue {
+	if len(labels) == 0 {
+		return nil
+	}
+	attrs := make([]attribute.KeyValue, 0, len(labels))
+	for k, v := range labels {
+		attrs = append(attrs, attribute.String(k, v))
+	}
+	return attrs
+}
+
+// Counter wraps an OTel Int64Counter.
+type Counter struct {
+	c metric.Int64Counter
+}
+
+// Add increments the counter by value.
+func (c *Counter) Add(ctx context.Context, value int64, labels map[string]string) {
+	c.c.Add(ctx, value, metric.WithAttributes(labelsToAttrs(labels)...))
+}
+
+// UpDownCounter wraps an OTel Int64UpDownCounter.
+type UpDownCounter struct {
+	c metric.Int64UpDownCounter
+}
+
+// Add adjusts the up-down counter by value.
+func (u *UpDownCounter) Add(ctx context.Context, value int64, labels map[string]string) {
+	u.c.Add(ctx, value, metric.WithAttributes(labelsToAttrs(labels)...))
+}
+
+// Int64Gauge wraps an OTel Int64Gauge.
+type Int64Gauge struct {
+	g metric.Int64Gauge
+}
+
+// Record sets the gauge to value.
+func (g *Int64Gauge) Record(ctx context.Context, value int64, labels map[string]string) {
+	g.g.Record(ctx, value, metric.WithAttributes(labelsToAttrs(labels)...))
+}
+
+// Float64Gauge wraps an OTel Float64Gauge.
+type Float64Gauge struct {
+	g metric.Float64Gauge
+}
+
+// Record sets the gauge to value.
+func (g *Float64Gauge) Record(ctx context.Context, value float64, labels map[string]string) {
+	g.g.Record(ctx, value, metric.WithAttributes(labelsToAttrs(labels)...))
+}
+
+// Histogram wraps an OTel Float64Histogram.
+type Histogram struct {
+	h metric.Float64Histogram
+}
+
+// Record observes value in the histogram.
+func (h *Histogram) Record(ctx context.Context, value float64, labels map[string]string) {
+	h.h.Record(ctx, value, metric.WithAttributes(labelsToAttrs(labels)...))
+}

internal/observability/otel/backend_test.go

@@ -0,0 +1,141 @@
+package otel_test
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	obsotel "github.com/fosrl/gerbil/internal/observability/otel"
+)
+
+const (
+	defaultGRPCEndpoint = "localhost:4317"
+	defaultServiceName  = "gerbil-test"
+)
+
+func newInMemoryBackend(t *testing.T) *obsotel.Backend {
+	t.Helper()
+	// Use a very short export interval; an in-process collector (noop exporter)
+	// is used by pointing to a non-existent endpoint with insecure mode.
+	// The backend itself should initialise without error since connection is lazy.
+	b, err := obsotel.New(obsotel.Config{
+		Protocol:       "grpc",
+		Endpoint:       defaultGRPCEndpoint,
+		Insecure:       true,
+		ExportInterval: 100 * time.Millisecond,
+		ServiceName:    defaultServiceName,
+		ServiceVersion: "0.0.1",
+	})
+	if err != nil {
+		t.Fatalf("failed to create otel backend: %v", err)
+	}
+	return b
+}
+
+func TestOtelBackendHTTPHandlerIsNil(t *testing.T) {
+	b := newInMemoryBackend(t)
+	defer b.Shutdown(context.Background()) //nolint:errcheck
+	if b.HTTPHandler() != nil {
+		t.Error("OTel backend HTTPHandler should return nil")
+	}
+}
+
+func TestOtelBackendShutdown(t *testing.T) {
+	b := newInMemoryBackend(t)
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
+	defer cancel()
+	if err := b.Shutdown(ctx); err != nil {
+		// Shutdown with unreachable collector may fail to flush; that's acceptable.
+		// What matters is that Shutdown does not panic.
+		t.Logf("Shutdown returned (expected with no collector): %v", err)
+	}
+}
+
+func TestOtelBackendCounter(t *testing.T) {
+	b := newInMemoryBackend(t)
+	defer b.Shutdown(context.Background()) //nolint:errcheck
+
+	c := b.NewCounter("gerbil_test_counter_total", "test counter", "result")
+	// Should not panic
+	c.Add(context.Background(), 1, map[string]string{"result": "ok"})
+	c.Add(context.Background(), 5, nil)
+}
+
+func TestOtelBackendUpDownCounter(t *testing.T) {
+	b := newInMemoryBackend(t)
+	defer b.Shutdown(context.Background()) //nolint:errcheck
+
+	u := b.NewUpDownCounter("gerbil_test_updown", "test updown", "state")
+	u.Add(context.Background(), 3, map[string]string{"state": "active"})
+	u.Add(context.Background(), -1, map[string]string{"state": "active"})
+}
+
+func TestOtelBackendInt64Gauge(t *testing.T) {
+	b := newInMemoryBackend(t)
+	defer b.Shutdown(context.Background()) //nolint:errcheck
+
+	g := b.NewInt64Gauge("gerbil_test_int_gauge", "test gauge")
+	g.Record(context.Background(), 42, nil)
+}
+
+func TestOtelBackendFloat64Gauge(t *testing.T) {
+	b := newInMemoryBackend(t)
+	defer b.Shutdown(context.Background()) //nolint:errcheck
+
+	g := b.NewFloat64Gauge("gerbil_test_float_gauge", "test float gauge")
+	g.Record(context.Background(), 3.14, nil)
+}
+
+func TestOtelBackendHistogram(t *testing.T) {
+	b := newInMemoryBackend(t)
+	defer b.Shutdown(context.Background()) //nolint:errcheck
+
+	h := b.NewHistogram("gerbil_test_duration_seconds", "test histogram",
+		[]float64{0.1, 0.5, 1.0}, "method")
+	h.Record(context.Background(), 0.3, map[string]string{"method": "GET"})
+}
+
+func TestOtelBackendHTTPProtocol(t *testing.T) {
+	b, err := obsotel.New(obsotel.Config{
+		Protocol:       "http",
+		Endpoint:       "localhost:4318",
+		Insecure:       true,
+		ExportInterval: 100 * time.Millisecond,
+		ServiceName:    defaultServiceName,
+	})
+	if err != nil {
+		t.Fatalf("failed to create otel http backend: %v", err)
+	}
+	defer b.Shutdown(context.Background()) //nolint:errcheck
+
+	if b.HTTPHandler() != nil {
+		t.Error("OTel HTTP backend should not expose a /metrics endpoint")
+	}
+}
+
+func TestOtelBackendInvalidProtocol(t *testing.T) {
+	_, err := obsotel.New(obsotel.Config{
+		Protocol:       "tcp",
+		Endpoint:       defaultGRPCEndpoint,
+		ExportInterval: 10 * time.Second,
+	})
+	if err == nil {
+		t.Error("expected error for invalid protocol")
+	}
+}
+
+func TestOtelBackendDeploymentEnvironment(t *testing.T) {
+	b, err := obsotel.New(obsotel.Config{
+		Protocol:              "grpc",
+		Endpoint:              defaultGRPCEndpoint,
+		Insecure:              true,
+		ExportInterval:        100 * time.Millisecond,
+		ServiceName:           defaultServiceName,
+		ServiceVersion:        "1.2.3",
+		DeploymentEnvironment: "staging",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer b.Shutdown(context.Background()) //nolint:errcheck
+}

internal/observability/otel/exporter.go

@@ -0,0 +1,50 @@
+package otel
+
+import (
+	"context"
+	"fmt"
+
+	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
+	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp"
+	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
+)
+
+// newExporter creates the appropriate OTLP exporter based on cfg.Protocol.
+func newExporter(ctx context.Context, cfg Config) (sdkmetric.Exporter, error) {
+	switch cfg.Protocol {
+	case "grpc", "":
+		return newGRPCExporter(ctx, cfg)
+	case "http":
+		return newHTTPExporter(ctx, cfg)
+	default:
+		return nil, fmt.Errorf("otel: unknown protocol %q (must be \"grpc\" or \"http\")", cfg.Protocol)
+	}
+}
+
+func newGRPCExporter(ctx context.Context, cfg Config) (sdkmetric.Exporter, error) {
+	opts := []otlpmetricgrpc.Option{
+		otlpmetricgrpc.WithEndpoint(cfg.Endpoint),
+	}
+	if cfg.Insecure {
+		opts = append(opts, otlpmetricgrpc.WithInsecure())
+	}
+	exp, err := otlpmetricgrpc.New(ctx, opts...)
+	if err != nil {
+		return nil, fmt.Errorf("otlp grpc exporter: %w", err)
+	}
+	return exp, nil
+}
+
+func newHTTPExporter(ctx context.Context, cfg Config) (sdkmetric.Exporter, error) {
+	opts := []otlpmetrichttp.Option{
+		otlpmetrichttp.WithEndpoint(cfg.Endpoint),
+	}
+	if cfg.Insecure {
+		opts = append(opts, otlpmetrichttp.WithInsecure())
+	}
+	exp, err := otlpmetrichttp.New(ctx, opts...)
+	if err != nil {
+		return nil, fmt.Errorf("otlp http exporter: %w", err)
+	}
+	return exp, nil
+}

internal/observability/otel/resource.go

@@ -0,0 +1,25 @@
+package otel
+
+import (
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk/resource"
+	semconv "go.opentelemetry.io/otel/semconv/v1.40.0"
+)
+
+// newResource builds an OTel resource for the Gerbil service.
+func newResource(serviceName, serviceVersion, deploymentEnv string) (*resource.Resource, error) {
+	attrs := []attribute.KeyValue{
+		semconv.ServiceName(serviceName),
+	}
+	if serviceVersion != "" {
+		attrs = append(attrs, semconv.ServiceVersion(serviceVersion))
+	}
+	if deploymentEnv != "" {
+		attrs = append(attrs, semconv.DeploymentEnvironmentName(deploymentEnv))
+	}
+
+	return resource.Merge(
+		resource.Default(),
+		resource.NewWithAttributes(semconv.SchemaURL, attrs...),
+	)
+}

internal/observability/prometheus/backend.go

@@ -0,0 +1,185 @@
+// Package prometheus implements the native Prometheus metrics backend for Gerbil.
+//
+// This backend uses the Prometheus Go client directly; it does NOT depend on the
+// OpenTelemetry SDK.  A dedicated Prometheus registry is used so that default
+// Go/process metrics are not unintentionally included unless the caller opts in.
+package prometheus
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+// Config holds Prometheus-backend configuration.
+type Config struct {
+	// Path is the HTTP endpoint path (e.g. "/metrics").
+	Path string
+
+	// IncludeGoMetrics controls whether the standard Go runtime and process
+	// collectors are registered on the dedicated registry.
+	// Defaults to true if not explicitly set.
+	IncludeGoMetrics *bool
+}
+
+// Backend is the native Prometheus metrics backend.
+// Metric instruments are created via the New* family of methods and stored
+// in the backend-specific instrument types that implement the observability
+// instrument interfaces.
+type Backend struct {
+	cfg      Config
+	registry *prometheus.Registry
+	handler  http.Handler
+}
+
+// New creates and initialises a Prometheus backend.
+//
+// cfg.Path sets the HTTP endpoint path (defaults to "/metrics" if empty).
+// cfg.IncludeGoMetrics controls whether standard Go runtime and process metrics
+// are included; defaults to true when nil.
+//
+// Returns an error if the registry cannot be created.
+func New(cfg Config) (*Backend, error) {
+	if cfg.Path == "" {
+		cfg.Path = "/metrics"
+	}
+
+	registry := prometheus.NewRegistry()
+
+	// Include Go and process metrics by default.
+	includeGo := cfg.IncludeGoMetrics == nil || *cfg.IncludeGoMetrics
+	if includeGo {
+		registry.MustRegister(
+			collectors.NewGoCollector(),
+			collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}),
+		)
+	}
+
+	handler := promhttp.HandlerFor(registry, promhttp.HandlerOpts{
+		EnableOpenMetrics: false,
+	})
+
+	return &Backend{cfg: cfg, registry: registry, handler: handler}, nil
+}
+
+// HTTPHandler returns the Prometheus /metrics HTTP handler.
+func (b *Backend) HTTPHandler() http.Handler {
+	return b.handler
+}
+
+// Shutdown is a no-op for the Prometheus backend.
+// The registry does not maintain background goroutines.
+func (b *Backend) Shutdown(_ context.Context) error {
+	_ = b
+	return nil
+}
+
+// NewCounter creates a Prometheus CounterVec registered on the backend's registry.
+func (b *Backend) NewCounter(name, desc string, labelNames ...string) *Counter {
+	vec := prometheus.NewCounterVec(prometheus.CounterOpts{
+		Name: name,
+		Help: desc,
+	}, labelNames)
+	b.registry.MustRegister(vec)
+	return &Counter{vec: vec}
+}
+
+// NewUpDownCounter creates a Prometheus GaugeVec (Prometheus gauges are
+// bidirectional) registered on the backend's registry.
+func (b *Backend) NewUpDownCounter(name, desc string, labelNames ...string) *UpDownCounter {
+	vec := prometheus.NewGaugeVec(prometheus.GaugeOpts{
+		Name: name,
+		Help: desc,
+	}, labelNames)
+	b.registry.MustRegister(vec)
+	return &UpDownCounter{vec: vec}
+}
+
+// NewInt64Gauge creates a Prometheus GaugeVec registered on the backend's registry.
+func (b *Backend) NewInt64Gauge(name, desc string, labelNames ...string) *Int64Gauge {
+	vec := prometheus.NewGaugeVec(prometheus.GaugeOpts{
+		Name: name,
+		Help: desc,
+	}, labelNames)
+	b.registry.MustRegister(vec)
+	return &Int64Gauge{vec: vec}
+}
+
+// NewFloat64Gauge creates a Prometheus GaugeVec registered on the backend's registry.
+func (b *Backend) NewFloat64Gauge(name, desc string, labelNames ...string) *Float64Gauge {
+	vec := prometheus.NewGaugeVec(prometheus.GaugeOpts{
+		Name: name,
+		Help: desc,
+	}, labelNames)
+	b.registry.MustRegister(vec)
+	return &Float64Gauge{vec: vec}
+}
+
+// NewHistogram creates a Prometheus HistogramVec registered on the backend's registry.
+func (b *Backend) NewHistogram(name, desc string, buckets []float64, labelNames ...string) *Histogram {
+	vec := prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Name:    name,
+		Help:    desc,
+		Buckets: buckets,
+	}, labelNames)
+	b.registry.MustRegister(vec)
+	return &Histogram{vec: vec}
+}
+
+// Counter is a native Prometheus counter instrument.
+type Counter struct {
+	vec *prometheus.CounterVec
+}
+
+// Add increments the counter by value for the given labels.
+//
+// value must be non-negative. Negative values are ignored.
+func (c *Counter) Add(_ context.Context, value int64, labels map[string]string) {
+	if value < 0 {
+		return
+	}
+	c.vec.With(prometheus.Labels(labels)).Add(float64(value))
+}
+
+// UpDownCounter is a native Prometheus gauge used as a bidirectional counter.
+type UpDownCounter struct {
+	vec *prometheus.GaugeVec
+}
+
+// Add adjusts the gauge by value for the given labels.
+func (u *UpDownCounter) Add(_ context.Context, value int64, labels map[string]string) {
+	u.vec.With(prometheus.Labels(labels)).Add(float64(value))
+}
+
+// Int64Gauge is a native Prometheus gauge recording integer snapshot values.
+type Int64Gauge struct {
+	vec *prometheus.GaugeVec
+}
+
+// Record sets the gauge to value for the given labels.
+func (g *Int64Gauge) Record(_ context.Context, value int64, labels map[string]string) {
+	g.vec.With(prometheus.Labels(labels)).Set(float64(value))
+}
+
+// Float64Gauge is a native Prometheus gauge recording float snapshot values.
+type Float64Gauge struct {
+	vec *prometheus.GaugeVec
+}
+
+// Record sets the gauge to value for the given labels.
+func (g *Float64Gauge) Record(_ context.Context, value float64, labels map[string]string) {
+	g.vec.With(prometheus.Labels(labels)).Set(value)
+}
+
+// Histogram is a native Prometheus histogram instrument.
+type Histogram struct {
+	vec *prometheus.HistogramVec
+}
+
+// Record observes value for the given labels.
+func (h *Histogram) Record(_ context.Context, value float64, labels map[string]string) {
+	h.vec.With(prometheus.Labels(labels)).Observe(value)
+}

internal/observability/prometheus/backend_test.go

@@ -0,0 +1,173 @@
+package prometheus_test
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	obsprom "github.com/fosrl/gerbil/internal/observability/prometheus"
+)
+
+func newTestBackend(t *testing.T) *obsprom.Backend {
+	t.Helper()
+	b, err := obsprom.New(obsprom.Config{Path: "/metrics"})
+	if err != nil {
+		t.Fatalf("failed to create prometheus backend: %v", err)
+	}
+	return b
+}
+
+func TestPrometheusBackendHTTPHandler(t *testing.T) {
+	b := newTestBackend(t)
+	if b.HTTPHandler() == nil {
+		t.Error("HTTPHandler should not be nil")
+	}
+}
+
+func TestPrometheusBackendShutdown(t *testing.T) {
+	b := newTestBackend(t)
+	if err := b.Shutdown(context.Background()); err != nil {
+		t.Errorf("Shutdown returned error: %v", err)
+	}
+}
+
+func TestPrometheusBackendCounter(t *testing.T) {
+	b := newTestBackend(t)
+	c := b.NewCounter("test_counter_total", "A test counter", "result")
+	c.Add(context.Background(), 3, map[string]string{"result": "ok"})
+
+	body := scrapeMetrics(t, b)
+	assertMetricPresent(t, body, `test_counter_total{result="ok"} 3`)
+}
+
+func TestPrometheusBackendUpDownCounter(t *testing.T) {
+	b := newTestBackend(t)
+	u := b.NewUpDownCounter("test_gauge_total", "A test up-down counter", "state")
+	u.Add(context.Background(), 5, map[string]string{"state": "active"})
+	u.Add(context.Background(), -2, map[string]string{"state": "active"})
+
+	body := scrapeMetrics(t, b)
+	assertMetricPresent(t, body, `test_gauge_total{state="active"} 3`)
+}
+
+func TestPrometheusBackendInt64Gauge(t *testing.T) {
+	b := newTestBackend(t)
+	g := b.NewInt64Gauge("test_int_gauge", "An integer gauge", "ifname")
+	g.Record(context.Background(), 42, map[string]string{"ifname": "wg0"})
+
+	body := scrapeMetrics(t, b)
+	assertMetricPresent(t, body, `test_int_gauge{ifname="wg0"} 42`)
+}
+
+func TestPrometheusBackendFloat64Gauge(t *testing.T) {
+	b := newTestBackend(t)
+	g := b.NewFloat64Gauge("test_float_gauge", "A float gauge", "cert")
+	g.Record(context.Background(), 7.5, map[string]string{"cert": "example.com"})
+
+	body := scrapeMetrics(t, b)
+	assertMetricPresent(t, body, `test_float_gauge{cert="example.com"} 7.5`)
+}
+
+func TestPrometheusBackendHistogram(t *testing.T) {
+	b := newTestBackend(t)
+	buckets := []float64{0.1, 0.5, 1.0, 5.0}
+	h := b.NewHistogram("test_duration_seconds", "A test histogram", buckets, "method")
+	h.Record(context.Background(), 0.3, map[string]string{"method": "GET"})
+
+	body := scrapeMetrics(t, b)
+	if !strings.Contains(body, "test_duration_seconds") {
+		t.Errorf("expected histogram metric in output, body:\n%s", body)
+	}
+}
+
+func TestPrometheusBackendMultipleLabels(t *testing.T) {
+	b := newTestBackend(t)
+	c := b.NewCounter("multi_label_total", "Multi-label counter", "method", "route", "status_code")
+	c.Add(context.Background(), 1, map[string]string{
+		"method":      "POST",
+		"route":       "/api/peers",
+		"status_code": "200",
+	})
+
+	body := scrapeMetrics(t, b)
+	if !strings.Contains(body, "multi_label_total") {
+		t.Errorf("expected multi_label_total in output, body:\n%s", body)
+	}
+}
+
+func TestPrometheusBackendGoMetrics(t *testing.T) {
+	b := newTestBackend(t)
+	body := scrapeMetrics(t, b)
+	// Default backend includes Go runtime metrics.
+	if !strings.Contains(body, "go_goroutines") {
+		t.Error("expected go_goroutines in default backend output")
+	}
+}
+
+func TestPrometheusBackendNoGoMetrics(t *testing.T) {
+	f := false
+	b, err := obsprom.New(obsprom.Config{IncludeGoMetrics: &f})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	body := scrapeMetrics(t, b)
+	if strings.Contains(body, "go_goroutines") {
+		t.Error("expected no go_goroutines when IncludeGoMetrics=false")
+	}
+}
+
+func TestPrometheusBackendNilLabels(t *testing.T) {
+	// Adding with nil labels should not panic (treated as empty map).
+	b := newTestBackend(t)
+	c := b.NewCounter("nil_labels_total", "counter with no labels")
+	// nil labels with no label names declared should be safe
+	c.Add(context.Background(), 1, nil)
+}
+
+func TestPrometheusBackendConcurrentAdd(t *testing.T) {
+	b := newTestBackend(t)
+	c := b.NewCounter("concurrent_total", "concurrent counter", "worker")
+
+	done := make(chan struct{})
+	for i := 0; i < 10; i++ {
+		go func(_ int) {
+			for j := 0; j < 100; j++ {
+				c.Add(context.Background(), 1, map[string]string{"worker": "w"})
+			}
+			done <- struct{}{}
+		}(i)
+	}
+	for i := 0; i < 10; i++ {
+		<-done
+	}
+
+	body := scrapeMetrics(t, b)
+	assertMetricPresent(t, body, `concurrent_total{worker="w"} 1000`)
+}
+
+// --- helpers ---
+
+func scrapeMetrics(t *testing.T, b *obsprom.Backend) string {
+	t.Helper()
+	req := httptest.NewRequest(http.MethodGet, "/metrics", http.NoBody)
+	rr := httptest.NewRecorder()
+	b.HTTPHandler().ServeHTTP(rr, req)
+	if rr.Code != http.StatusOK {
+		t.Fatalf("metrics handler returned %d", rr.Code)
+	}
+	body, err := io.ReadAll(rr.Body)
+	if err != nil {
+		t.Fatalf("failed to read response body: %v", err)
+	}
+	return string(body)
+}
+
+func assertMetricPresent(t *testing.T, body, expected string) {
+	t.Helper()
+	if !strings.Contains(body, expected) {
+		t.Errorf("expected %q in metrics output\nbody:\n%s", expected, body)
+	}
+}

main.go

@@ -23,6 +23,7 @@ import (
 	"syscall"
 	"time"
 
+	"github.com/fosrl/gerbil/internal/metrics"
 	"github.com/fosrl/gerbil/logger"
 	"github.com/fosrl/gerbil/proxy"
 	"github.com/fosrl/gerbil/relay"
@@ -42,6 +43,9 @@ var (
 	notifyURL        string
 	proxyRelay       *relay.UDPProxyServer
 	proxySNI         *proxy.SNIProxy
+	doTrafficShaping bool
+	bandwidthLimit   string
+	ifbName          string // IFB device name for ingress traffic shaping
 )
 
 type WgConfig struct {
@@ -98,6 +102,35 @@ type UpdateDestinationsRequest struct {
 	Destinations []relay.PeerDestination `json:"destinations"`
 }
 
+// httpMetricsMiddleware wraps HTTP handlers with metrics tracking
+func httpMetricsMiddleware(endpoint string, handler http.HandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		startTime := time.Now()
+
+		// Create a response writer wrapper to capture status code
+		ww := &responseWriterWrapper{ResponseWriter: w, statusCode: http.StatusOK}
+
+		// Call the actual handler
+		handler(ww, r)
+
+		// Record metrics
+		duration := time.Since(startTime).Seconds()
+		metrics.RecordHTTPRequest(endpoint, r.Method, fmt.Sprintf("%d", ww.statusCode))
+		metrics.RecordHTTPRequestDuration(endpoint, r.Method, duration)
+	}
+}
+
+// responseWriterWrapper wraps http.ResponseWriter to capture status code
+type responseWriterWrapper struct {
+	http.ResponseWriter
+	statusCode int
+}
+
+func (w *responseWriterWrapper) WriteHeader(statusCode int) {
+	w.statusCode = statusCode
+	w.ResponseWriter.WriteHeader(statusCode)
+}
+
 func parseLogLevel(level string) logger.LogLevel {
 	switch strings.ToUpper(level) {
 	case "DEBUG":
@@ -133,6 +166,15 @@ func main() {
 		localOverridesStr    string
 		trustedUpstreamsStr  string
 		proxyProtocol        bool
+
+		// Metrics configuration variables (set from env, then overridden by CLI flags)
+		metricsEnabled            bool
+		metricsBackend            string
+		metricsPath               string
+		otelMetricsProtocol       string
+		otelMetricsEndpoint       string
+		otelMetricsInsecure       bool
+		otelMetricsExportInterval time.Duration
 	)
 
 	interfaceName = os.Getenv("INTERFACE")
@@ -151,6 +193,42 @@ func main() {
 	localOverridesStr = os.Getenv("LOCAL_OVERRIDES")
 	trustedUpstreamsStr = os.Getenv("TRUSTED_UPSTREAMS")
 	proxyProtocolStr := os.Getenv("PROXY_PROTOCOL")
+	doTrafficShapingStr := os.Getenv("DO_TRAFFIC_SHAPING")
+	bandwidthLimitStr := os.Getenv("BANDWIDTH_LIMIT")
+
+	// Read metrics env vars (defaults applied by DefaultMetricsConfig; these override defaults).
+	metricsEnabled = true // default
+	if v := os.Getenv("METRICS_ENABLED"); v != "" {
+		metricsEnabled = strings.ToLower(v) == "true"
+	}
+	metricsBackend = "prometheus" // default
+	if v := os.Getenv("METRICS_BACKEND"); v != "" {
+		metricsBackend = v
+	}
+	metricsPath = "/metrics" // default
+	if v := os.Getenv("METRICS_PATH"); v != "" {
+		metricsPath = v
+	}
+	otelMetricsProtocol = "grpc" // default
+	if v := os.Getenv("OTEL_METRICS_PROTOCOL"); v != "" {
+		otelMetricsProtocol = v
+	}
+	otelMetricsEndpoint = "localhost:4317" // default
+	if v := os.Getenv("OTEL_METRICS_ENDPOINT"); v != "" {
+		otelMetricsEndpoint = v
+	}
+	otelMetricsInsecure = true // default
+	if v := os.Getenv("OTEL_METRICS_INSECURE"); v != "" {
+		otelMetricsInsecure = strings.ToLower(v) == "true"
+	}
+	otelMetricsExportInterval = 60 * time.Second // default
+	if v := os.Getenv("OTEL_METRICS_EXPORT_INTERVAL"); v != "" {
+		if d, err2 := time.ParseDuration(v); err2 == nil {
+			otelMetricsExportInterval = d
+		} else {
+			log.Printf("WARN: invalid OTEL_METRICS_EXPORT_INTERVAL=%q: %v", v, err2)
+		}
+	}
 
 	if interfaceName == "" {
 		flag.StringVar(&interfaceName, "interface", "wg0", "Name of the WireGuard interface")
@@ -222,11 +300,72 @@ func main() {
 		flag.BoolVar(&proxyProtocol, "proxy-protocol", true, "Enable PROXY protocol v1 for preserving client IP")
 	}
 
+	if doTrafficShapingStr != "" {
+		doTrafficShaping = strings.ToLower(doTrafficShapingStr) == "true"
+	}
+	if doTrafficShapingStr == "" {
+		flag.BoolVar(&doTrafficShaping, "do-traffic-shaping", false, "Whether to set up traffic shaping rules for peers (requires tc command and root privileges)")
+	}
+
+	if bandwidthLimitStr != "" {
+		bandwidthLimit = bandwidthLimitStr
+	}
+	if bandwidthLimitStr == "" {
+		flag.StringVar(&bandwidthLimit, "bandwidth-limit", "50mbit", "Bandwidth limit per peer for traffic shaping (e.g. 50mbit, 1gbit)")
+	}
+
+	// Metrics CLI flags – always registered so that CLI overrides env/defaults.
+	flag.BoolVar(&metricsEnabled, "metrics-enabled", metricsEnabled, "Enable metrics collection (default: true)")
+	flag.StringVar(&metricsBackend, "metrics-backend", metricsBackend, "Metrics backend: prometheus, otel, or none")
+	flag.StringVar(&metricsPath, "metrics-path", metricsPath, "HTTP path for Prometheus /metrics endpoint")
+	flag.StringVar(&otelMetricsProtocol, "otel-metrics-protocol", otelMetricsProtocol, "OTLP transport protocol: grpc or http")
+	flag.StringVar(&otelMetricsEndpoint, "otel-metrics-endpoint", otelMetricsEndpoint, "OTLP collector endpoint (e.g. localhost:4317)")
+	flag.BoolVar(&otelMetricsInsecure, "otel-metrics-insecure", otelMetricsInsecure, "Disable TLS for OTLP connection")
+	flag.DurationVar(&otelMetricsExportInterval, "otel-metrics-export-interval", otelMetricsExportInterval, "Interval between OTLP metric pushes")
+
 	flag.Parse()
 
+	// Derive IFB device name from the WireGuard interface name (Linux limit: 15 chars)
+	ifbName = "ifb_" + interfaceName
+	if len(ifbName) > 15 {
+		ifbName = ifbName[:15]
+	}
+
 	logger.Init()
 	logger.GetLogger().SetLevel(parseLogLevel(logLevel))
 
+	// Initialize metrics with the selected backend.
+	// Config precedence: CLI flags > env vars > defaults (already applied above).
+	metricsHandler, err := metrics.Initialize(metrics.Config{
+		Enabled: metricsEnabled,
+		Backend: metricsBackend,
+		Prometheus: metrics.PrometheusConfig{
+			Path: metricsPath,
+		},
+		OTel: metrics.OTelConfig{
+			Protocol:       otelMetricsProtocol,
+			Endpoint:       otelMetricsEndpoint,
+			Insecure:       otelMetricsInsecure,
+			ExportInterval: otelMetricsExportInterval,
+		},
+		ServiceName:           "gerbil",
+		ServiceVersion:        "1.0.0",
+		DeploymentEnvironment: os.Getenv("DEPLOYMENT_ENVIRONMENT"),
+	})
+	if err != nil {
+		logger.Fatal("Failed to initialize metrics: %v", err)
+	}
+	defer func() {
+		shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer cancel()
+		if err := metrics.Shutdown(shutdownCtx); err != nil {
+			logger.Error("Failed to shutdown metrics: %v", err)
+		}
+	}()
+
+	// Record restart metric
+	metrics.RecordRestart()
+
 	// Base context for the application; cancel on SIGINT/SIGTERM
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer stop()
@@ -335,6 +474,13 @@ func main() {
 		logger.Fatal("Failed to ensure WireGuard interface: %v", err)
 	}
 
+	// Set up IFB device for bidirectional ingress/egress traffic shaping if enabled
+	if doTrafficShaping {
+		if err := ensureIFBDevice(); err != nil {
+			logger.Fatal("Failed to ensure IFB device for traffic shaping: %v", err)
+		}
+	}
+
 	// Ensure the WireGuard peers exist
 	ensureWireguardPeers(wgconfig.Peers)
 
@@ -388,18 +534,27 @@ func main() {
 		logger.Fatal("Failed to start proxy: %v", err)
 	}
 
-	// Set up HTTP server
+	// Set up HTTP server with metrics middleware
-	http.HandleFunc("/peer", handlePeer)
+	http.HandleFunc("/peer", httpMetricsMiddleware("peer", handlePeer))
-	http.HandleFunc("/update-proxy-mapping", handleUpdateProxyMapping)
+	http.HandleFunc("/update-proxy-mapping", httpMetricsMiddleware("update_proxy_mapping", handleUpdateProxyMapping))
-	http.HandleFunc("/update-destinations", handleUpdateDestinations)
+	http.HandleFunc("/update-destinations", httpMetricsMiddleware("update_destinations", handleUpdateDestinations))
-	http.HandleFunc("/update-local-snis", handleUpdateLocalSNIs)
+	http.HandleFunc("/update-local-snis", httpMetricsMiddleware("update_local_snis", handleUpdateLocalSNIs))
-	http.HandleFunc("/healthz", handleHealthz)
+	http.HandleFunc("/healthz", httpMetricsMiddleware("healthz", handleHealthz))
+
+	// Register metrics endpoint only for Prometheus backend.
+	// OTel backend pushes to a collector; no /metrics endpoint needed.
+	if metricsHandler != nil {
+		http.Handle(metricsPath, metricsHandler)
+		logger.Info("Metrics endpoint enabled at %s", metricsPath)
+	}
+
 	logger.Info("Starting HTTP server on %s", listenAddr)
 
 	// HTTP server with graceful shutdown on context cancel
 	server := &http.Server{
 		Addr:              listenAddr,
 		Handler:           nil,
+		ReadHeaderTimeout: 3 * time.Second,
 	}
 	group.Go(func() error {
 		// http.ErrServerClosed is returned on graceful shutdown; not an error for us
@@ -434,26 +589,35 @@ func main() {
 func loadRemoteConfig(url string, key wgtypes.Key, reachableAt string) (WgConfig, error) {
 	var body *bytes.Buffer
 	if reachableAt == "" {
-		body = bytes.NewBuffer([]byte(fmt.Sprintf(`{"publicKey": "%s"}`, key.PublicKey().String())))
+		body = bytes.NewBuffer([]byte(fmt.Sprintf(`{"publicKey": %q}`, key.PublicKey().String())))
 	} else {
-		body = bytes.NewBuffer([]byte(fmt.Sprintf(`{"publicKey": "%s", "reachableAt": "%s"}`, key.PublicKey().String(), reachableAt)))
+		body = bytes.NewBuffer([]byte(fmt.Sprintf(`{"publicKey": %q, "reachableAt": %q}`, key.PublicKey().String(), reachableAt)))
 	}
 	resp, err := http.Post(url, "application/json", body)
 	if err != nil {
 		// print the error
 		logger.Error("Error fetching remote config %s: %v", url, err)
+		// Record remote config fetch error
+		metrics.RecordRemoteConfigFetch("error")
 		return WgConfig{}, err
 	}
 	defer resp.Body.Close()
 
 	data, err := io.ReadAll(resp.Body)
 	if err != nil {
+		metrics.RecordRemoteConfigFetch("error")
 		return WgConfig{}, err
 	}
 
 	var config WgConfig
 	err = json.Unmarshal(data, &config)
+	if err != nil {
+		metrics.RecordRemoteConfigFetch("error")
+		return config, err
+	}
 
+	// Record successful remote config fetch
+	metrics.RecordRemoteConfigFetch("success")
 	return config, err
 }
 
@@ -561,6 +725,10 @@ func ensureWireguardInterface(wgconfig WgConfig) error {
 
 	logger.Info("WireGuard interface %s created and configured", interfaceName)
 
+	// Record interface state metric
+	hostname, _ := os.Hostname()
+	metrics.RecordInterfaceUp(interfaceName, hostname, true)
+
 	return nil
 }
 
@@ -858,15 +1026,22 @@ func handleAddPeer(w http.ResponseWriter, r *http.Request) {
 	var peer Peer
 	if err := json.NewDecoder(r.Body).Decode(&peer); err != nil {
 		http.Error(w, err.Error(), http.StatusBadRequest)
+		// Record peer add error
+		metrics.RecordPeerOperation("add", "error")
 		return
 	}
 
 	err := addPeer(peer)
 	if err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
+		// Record peer add error
+		metrics.RecordPeerOperation("add", "error")
 		return
 	}
 
+	// Record peer add success
+	metrics.RecordPeerOperation("add", "success")
+
 	// Notify if notifyURL is set
 	go notifyPeerChange("add", peer.PublicKey)
 
@@ -886,17 +1061,23 @@ func addPeerInternal(peer Peer) error {
 		return fmt.Errorf("failed to parse public key: %v", err)
 	}
 
+	logger.Debug("Adding peer %s with AllowedIPs: %v", peer.PublicKey, peer.AllowedIPs)
+
 	// parse allowed IPs into array of net.IPNet
 	var allowedIPs []net.IPNet
 	var wgIPs []string
 	for _, ipStr := range peer.AllowedIPs {
+		logger.Debug("Parsing AllowedIP: %s", ipStr)
 		_, ipNet, err := net.ParseCIDR(ipStr)
 		if err != nil {
+			logger.Warn("Failed to parse allowed IP '%s' for peer %s: %v", ipStr, peer.PublicKey, err)
 			return fmt.Errorf("failed to parse allowed IP: %v", err)
 		}
 		allowedIPs = append(allowedIPs, *ipNet)
 		// Extract the IP address from the CIDR for relay cleanup
-		wgIPs = append(wgIPs, ipNet.IP.String())
+		extractedIP := ipNet.IP.String()
+		wgIPs = append(wgIPs, extractedIP)
+		logger.Debug("Extracted IP %s from AllowedIP %s", extractedIP, ipStr)
 	}
 
 	peerConfig := wgtypes.PeerConfig{
@@ -912,6 +1093,18 @@ func addPeerInternal(peer Peer) error {
 		return fmt.Errorf("failed to add peer: %v", err)
 	}
 
+	// Setup bandwidth limiting for each peer IP
+	if doTrafficShaping {
+		logger.Debug("doTrafficShaping is true, setting up bandwidth limits for %d IPs", len(wgIPs))
+		for _, wgIP := range wgIPs {
+			if err := setupPeerBandwidthLimit(wgIP); err != nil {
+				logger.Warn("Failed to setup bandwidth limit for peer IP %s: %v", wgIP, err)
+			}
+		}
+	} else {
+		logger.Debug("doTrafficShaping is false, skipping bandwidth limit setup")
+	}
+
 	// Clear relay connections for the peer's WireGuard IPs
 	if proxyRelay != nil {
 		for _, wgIP := range wgIPs {
@@ -921,6 +1114,10 @@ func addPeerInternal(peer Peer) error {
 
 	logger.Info("Peer %s added successfully", peer.PublicKey)
 
+	// Record metrics
+	metrics.RecordPeersTotal(interfaceName, 1)
+	metrics.RecordAllowedIPsCount(interfaceName, peer.PublicKey, int64(len(peer.AllowedIPs)))
+
 	return nil
 }
 
@@ -928,15 +1125,22 @@ func handleRemovePeer(w http.ResponseWriter, r *http.Request) {
 	publicKey := r.URL.Query().Get("public_key")
 	if publicKey == "" {
 		http.Error(w, "Missing public_key query parameter", http.StatusBadRequest)
+		// Record peer remove error
+		metrics.RecordPeerOperation("remove", "error")
 		return
 	}
 
 	err := removePeer(publicKey)
 	if err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
+		// Record peer remove error
+		metrics.RecordPeerOperation("remove", "error")
 		return
 	}
 
+	// Record peer remove success
+	metrics.RecordPeerOperation("remove", "success")
+
 	// Notify if notifyURL is set
 	go notifyPeerChange("remove", publicKey)
 
@@ -956,9 +1160,8 @@ func removePeerInternal(publicKey string) error {
 		return fmt.Errorf("failed to parse public key: %v", err)
 	}
 
-	// Get current peer info before removing to clear relay connections
+	// Get current peer info before removing to clear relay connections and bandwidth limits
 	var wgIPs []string
-	if proxyRelay != nil {
 	device, err := wgClient.Device(interfaceName)
 	if err == nil {
 		for _, peer := range device.Peers {
@@ -971,7 +1174,6 @@ func removePeerInternal(publicKey string) error {
 			}
 		}
 	}
-	}
 
 	peerConfig := wgtypes.PeerConfig{
 		PublicKey: pubKey,
@@ -986,6 +1188,15 @@ func removePeerInternal(publicKey string) error {
 		return fmt.Errorf("failed to remove peer: %v", err)
 	}
 
+	// Remove bandwidth limits for each peer IP
+	if doTrafficShaping {
+		for _, wgIP := range wgIPs {
+			if err := removePeerBandwidthLimit(wgIP); err != nil {
+				logger.Warn("Failed to remove bandwidth limit for peer IP %s: %v", wgIP, err)
+			}
+		}
+	}
+
 	// Clear relay connections for the peer's WireGuard IPs
 	if proxyRelay != nil {
 		for _, wgIP := range wgIPs {
@@ -995,6 +1206,10 @@ func removePeerInternal(publicKey string) error {
 
 	logger.Info("Peer %s removed successfully", publicKey)
 
+	// Record metrics
+	metrics.RecordPeersTotal(interfaceName, -1)
+	metrics.RecordAllowedIPsCount(interfaceName, publicKey, -int64(len(wgIPs)))
+
 	return nil
 }
 
@@ -1029,6 +1244,8 @@ func handleUpdateProxyMapping(w http.ResponseWriter, r *http.Request) {
 	if proxyRelay == nil {
 		logger.Error("Proxy server is not available")
 		http.Error(w, "Proxy server is not available", http.StatusInternalServerError)
+		// Record error
+		metrics.RecordProxyMappingUpdateRequest("error")
 		return
 	}
 
@@ -1039,6 +1256,9 @@ func handleUpdateProxyMapping(w http.ResponseWriter, r *http.Request) {
 		update.OldDestination.DestinationIP, update.OldDestination.DestinationPort,
 		update.NewDestination.DestinationIP, update.NewDestination.DestinationPort)
 
+	// Record success
+	metrics.RecordProxyMappingUpdateRequest("success")
+
 	w.WriteHeader(http.StatusOK)
 	json.NewEncoder(w).Encode(map[string]interface{}{
 		"status":         "Proxy mappings updated successfully",
@@ -1099,6 +1319,8 @@ func handleUpdateDestinations(w http.ResponseWriter, r *http.Request) {
 	if proxyRelay == nil {
 		logger.Error("Proxy server is not available")
 		http.Error(w, "Proxy server is not available", http.StatusInternalServerError)
+		// Record error
+		metrics.RecordDestinationsUpdateRequest("error")
 		return
 	}
 
@@ -1107,6 +1329,9 @@ func handleUpdateDestinations(w http.ResponseWriter, r *http.Request) {
 	logger.Info("Updated proxy mapping for %s:%d with %d destinations",
 		request.SourceIP, request.SourcePort, len(request.Destinations))
 
+	// Record success
+	metrics.RecordDestinationsUpdateRequest("success")
+
 	w.WriteHeader(http.StatusOK)
 	json.NewEncoder(w).Encode(map[string]interface{}{
 		"status":           "Destinations updated successfully",
@@ -1168,7 +1393,7 @@ func calculatePeerBandwidth() ([]PeerBandwidth, error) {
 		return nil, fmt.Errorf("failed to get device: %v", err)
 	}
 
-	peerBandwidths := []PeerBandwidth{}
+	var peerBandwidths []PeerBandwidth
 	now := time.Now()
 
 	mu.Lock()
@@ -1209,6 +1434,14 @@ func calculatePeerBandwidth() ([]PeerBandwidth, error) {
 				bytesInMB := bytesInDiff / (1024 * 1024)
 				bytesOutMB := bytesOutDiff / (1024 * 1024)
 
+				// Record metrics (in bytes)
+				if bytesInDiff > 0 {
+					metrics.RecordBytesReceived(interfaceName, publicKey, int64(bytesInDiff))
+				}
+				if bytesOutDiff > 0 {
+					metrics.RecordBytesTransmitted(interfaceName, publicKey, int64(bytesOutDiff))
+				}
+
 				peerBandwidths = append(peerBandwidths, PeerBandwidth{
 					PublicKey: publicKey,
 					BytesIn:   bytesInMB,
@@ -1248,24 +1481,31 @@ func calculatePeerBandwidth() ([]PeerBandwidth, error) {
 func reportPeerBandwidth(apiURL string) error {
 	bandwidths, err := calculatePeerBandwidth()
 	if err != nil {
+		// Record bandwidth report error
+		metrics.RecordBandwidthReport("error")
 		return fmt.Errorf("failed to calculate peer bandwidth: %v", err)
 	}
 
 	jsonData, err := json.Marshal(bandwidths)
 	if err != nil {
+		metrics.RecordBandwidthReport("error")
 		return fmt.Errorf("failed to marshal bandwidth data: %v", err)
 	}
 
 	resp, err := http.Post(apiURL, "application/json", bytes.NewBuffer(jsonData))
 	if err != nil {
+		metrics.RecordBandwidthReport("error")
 		return fmt.Errorf("failed to send bandwidth data: %v", err)
 	}
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
+		metrics.RecordBandwidthReport("error")
 		return fmt.Errorf("API returned non-OK status: %s", resp.Status)
 	}
 
+	// Record successful bandwidth report
+	metrics.RecordBandwidthReport("success")
 	return nil
 }
 
@@ -1299,14 +1539,25 @@ func monitorMemory(limit uint64) {
 	for {
 		runtime.ReadMemStats(&m)
 		if m.Alloc > limit {
+			// Determine severity based on how much over the limit
+			severity := "warning"
+			if m.Alloc > limit*2 {
+				severity = "critical"
+			}
+
 			fmt.Printf("Memory spike detected (%d bytes). Dumping profile...\n", m.Alloc)
 
+			// Record memory spike metric
+			metrics.RecordMemorySpike(severity)
+
 			f, err := os.Create(fmt.Sprintf("/var/config/heap/heap-spike-%d.pprof", time.Now().Unix()))
 			if err != nil {
 				log.Println("could not create profile:", err)
 			} else {
 				pprof.WriteHeapProfile(f)
 				f.Close()
+				// Record heap profile written metric
+				metrics.RecordHeapProfileWritten()
 			}
 
 			// Wait a while before checking again to avoid spamming profiles
@@ -1315,3 +1566,306 @@ func monitorMemory(limit uint64) {
 		time.Sleep(5 * time.Second)
 	}
 }
+
+// ensureIFBDevice creates and configures the IFB (Intermediate Functional Block) device used to
+// shape ingress traffic on the WireGuard interface. Linux TC qdiscs only control egress by default;
+// the IFB trick redirects all ingress packets to a virtual device so HTB shaping can be applied
+// there, and the packets are transparently re-injected into the kernel network stack afterwards.
+// This is completely invisible to sockets/applications (including a reverse proxy on the host).
+func ensureIFBDevice() error {
+	// Check if the ifb kernel module is loaded (works inside containers too)
+	if _, err := os.Stat("/sys/module/ifb"); os.IsNotExist(err) {
+		logger.Warn("IFB module not loaded, skipping IFB setup and ingress traffic shaping")
+		return nil
+	}
+
+	// Create the IFB device if it does not already exist
+	_, err := netlink.LinkByName(ifbName)
+	if err != nil {
+		if _, ok := err.(netlink.LinkNotFoundError); ok {
+			cmd := exec.Command("ip", "link", "add", ifbName, "type", "ifb")
+			if out, err := cmd.CombinedOutput(); err != nil {
+				return fmt.Errorf("failed to create IFB device %s: %v, output: %s", ifbName, err, string(out))
+			}
+			logger.Info("Created IFB device %s", ifbName)
+		} else {
+			return fmt.Errorf("failed to look up IFB device %s: %v", ifbName, err)
+		}
+	} else {
+		logger.Info("IFB device %s already exists", ifbName)
+	}
+
+	// Bring the IFB device up
+	cmd := exec.Command("ip", "link", "set", "dev", ifbName, "up")
+	if out, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("failed to bring up IFB device %s: %v, output: %s", ifbName, err, string(out))
+	}
+
+	// Attach an ingress qdisc to the WireGuard interface if one is not already present
+	cmd = exec.Command("tc", "qdisc", "show", "dev", interfaceName)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("failed to query qdiscs on %s: %v", interfaceName, err)
+	}
+	if !strings.Contains(string(out), "ingress") {
+		cmd = exec.Command("tc", "qdisc", "add", "dev", interfaceName, "handle", "ffff:", "ingress")
+		if out, err := cmd.CombinedOutput(); err != nil {
+			return fmt.Errorf("failed to add ingress qdisc to %s: %v, output: %s", interfaceName, err, string(out))
+		}
+		logger.Info("Added ingress qdisc to %s", interfaceName)
+	}
+
+	// Add a catch-all filter that redirects every ingress packet from wg0 to the IFB device.
+	// Per-peer rate limiting then happens on ifb0's egress HTB qdisc (handle 2:).
+	cmd = exec.Command("tc", "filter", "show", "dev", interfaceName, "parent", "ffff:")
+	out, err = cmd.CombinedOutput()
+	if err != nil || !strings.Contains(string(out), ifbName) {
+		cmd = exec.Command("tc", "filter", "add", "dev", interfaceName,
+			"parent", "ffff:", "protocol", "ip",
+			"u32", "match", "u32", "0", "0",
+			"action", "mirred", "egress", "redirect", "dev", ifbName)
+		if out, err := cmd.CombinedOutput(); err != nil {
+			return fmt.Errorf("failed to add ingress redirect filter on %s: %v, output: %s", interfaceName, err, string(out))
+		}
+		logger.Info("Added ingress redirect filter: %s -> %s", interfaceName, ifbName)
+	}
+
+	// Ensure an HTB root qdisc exists on the IFB device (handle 2:) for per-peer shaping
+	cmd = exec.Command("tc", "qdisc", "show", "dev", ifbName)
+	out, err = cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("failed to query qdiscs on %s: %v", ifbName, err)
+	}
+	if !strings.Contains(string(out), "htb") {
+		cmd = exec.Command("tc", "qdisc", "add", "dev", ifbName, "root", "handle", "2:", "htb", "default", "9999")
+		if out, err := cmd.CombinedOutput(); err != nil {
+			return fmt.Errorf("failed to add HTB qdisc to %s: %v, output: %s", ifbName, err, string(out))
+		}
+		logger.Info("Added HTB root qdisc (handle 2:) to IFB device %s", ifbName)
+	}
+
+	logger.Info("IFB device %s ready for ingress traffic shaping", ifbName)
+	return nil
+}
+
+// setupPeerBandwidthLimit sets up TC (Traffic Control) to limit bandwidth for a specific peer IP
+// Bandwidth limit is configurable via the --bandwidth-limit flag or BANDWIDTH_LIMIT env var (default: 50mbit)
+func setupPeerBandwidthLimit(peerIP string) error {
+	logger.Debug("setupPeerBandwidthLimit called for peer IP: %s", peerIP)
+
+	// Parse the IP to get just the IP address (strip any CIDR notation if present)
+	ip := peerIP
+	if strings.Contains(peerIP, "/") {
+		parsedIP, _, err := net.ParseCIDR(peerIP)
+		if err != nil {
+			return fmt.Errorf("failed to parse peer IP: %v", err)
+		}
+		ip = parsedIP.String()
+	}
+
+	// First, ensure we have a root qdisc on the interface (HTB - Hierarchical Token Bucket)
+	// Check if qdisc already exists
+	cmd := exec.Command("tc", "qdisc", "show", "dev", interfaceName)
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("failed to check qdisc: %v, output: %s", err, string(output))
+	}
+
+	// If no HTB qdisc exists, create one
+	if !strings.Contains(string(output), "htb") {
+		cmd = exec.Command("tc", "qdisc", "add", "dev", interfaceName, "root", "handle", "1:", "htb", "default", "9999")
+		if output, err := cmd.CombinedOutput(); err != nil {
+			return fmt.Errorf("failed to add root qdisc: %v, output: %s", err, string(output))
+		}
+		logger.Info("Created HTB root qdisc on %s", interfaceName)
+	}
+
+	// Generate a unique class ID based on the IP address
+	// We'll use the last octet of the IP as part of the class ID
+	ipParts := strings.Split(ip, ".")
+	if len(ipParts) != 4 {
+		return fmt.Errorf("invalid IPv4 address: %s", ip)
+	}
+	lastOctet := ipParts[3]
+	classID := fmt.Sprintf("1:%s", lastOctet)
+	logger.Debug("Generated class ID %s for peer IP %s", classID, ip)
+
+	// Create a class for this peer with bandwidth limit
+	cmd = exec.Command("tc", "class", "add", "dev", interfaceName, "parent", "1:", "classid", classID,
+		"htb", "rate", bandwidthLimit, "ceil", bandwidthLimit)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		logger.Debug("tc class add failed for %s: %v, output: %s", ip, err, string(output))
+		// If class already exists, try to replace it
+		if strings.Contains(string(output), "File exists") {
+			cmd = exec.Command("tc", "class", "replace", "dev", interfaceName, "parent", "1:", "classid", classID,
+				"htb", "rate", bandwidthLimit, "ceil", bandwidthLimit)
+			if output, err := cmd.CombinedOutput(); err != nil {
+				return fmt.Errorf("failed to replace class: %v, output: %s", err, string(output))
+			}
+			logger.Debug("Successfully replaced existing class %s for peer IP %s", classID, ip)
+		} else {
+			return fmt.Errorf("failed to add class: %v, output: %s", err, string(output))
+		}
+	} else {
+		logger.Debug("Successfully added new class %s for peer IP %s", classID, ip)
+	}
+
+	// Add a filter to match traffic to this peer IP on wg0 egress (peer's download)
+	cmd = exec.Command("tc", "filter", "add", "dev", interfaceName, "protocol", "ip", "parent", "1:",
+		"prio", "1", "u32", "match", "ip", "dst", ip, "flowid", classID)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		logger.Warn("Failed to add egress filter for peer IP %s: %v, output: %s", ip, err, string(output))
+	}
+
+	// Set up ingress shaping on the IFB device (peer's upload / ingress on wg0).
+	// All wg0 ingress is redirected to ifb0 by ensureIFBDevice; we add a per-peer
+	// class + src filter here so each peer gets its own independent rate limit.
+	ifbClassID := fmt.Sprintf("2:%s", lastOctet)
+
+	// Check if the ifb kernel module is loaded (works inside containers too)
+	if _, err := os.Stat("/sys/module/ifb"); os.IsNotExist(err) {
+		logger.Warn("IFB module not loaded, skipping IFB setup and ingress traffic shaping.")
+		logger.Info("Setup bandwidth limit of %s for peer IP %s (egress class %s, ingress class %s)", bandwidthLimit, ip, classID, ifbClassID)
+		return nil
+	}
+
+	cmd = exec.Command("tc", "class", "add", "dev", ifbName, "parent", "2:", "classid", ifbClassID,
+		"htb", "rate", bandwidthLimit, "ceil", bandwidthLimit)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		if strings.Contains(string(output), "File exists") {
+			cmd = exec.Command("tc", "class", "replace", "dev", ifbName, "parent", "2:", "classid", ifbClassID,
+				"htb", "rate", bandwidthLimit, "ceil", bandwidthLimit)
+			if output, err := cmd.CombinedOutput(); err != nil {
+				logger.Warn("Failed to replace IFB class for peer IP %s: %v, output: %s", ip, err, string(output))
+			} else {
+				logger.Debug("Replaced existing IFB class %s for peer IP %s", ifbClassID, ip)
+			}
+		} else {
+			logger.Warn("Failed to add IFB class for peer IP %s: %v, output: %s", ip, err, string(output))
+		}
+	} else {
+		logger.Debug("Added IFB class %s for peer IP %s", ifbClassID, ip)
+	}
+
+	cmd = exec.Command("tc", "filter", "add", "dev", ifbName, "protocol", "ip", "parent", "2:",
+		"prio", "1", "u32", "match", "ip", "src", ip, "flowid", ifbClassID)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		logger.Warn("Failed to add IFB ingress filter for peer IP %s: %v, output: %s", ip, err, string(output))
+	}
+
+	logger.Info("Setup bandwidth limit of %s for peer IP %s (egress class %s, ingress class %s)", bandwidthLimit, ip, classID, ifbClassID)
+	return nil
+}
+
+// removePeerBandwidthLimit removes TC rules for a specific peer IP
+func removePeerBandwidthLimit(peerIP string) error {
+	// Parse the IP to get just the IP address
+	ip := peerIP
+	if strings.Contains(peerIP, "/") {
+		parsedIP, _, err := net.ParseCIDR(peerIP)
+		if err != nil {
+			return fmt.Errorf("failed to parse peer IP: %v", err)
+		}
+		ip = parsedIP.String()
+	}
+
+	// Generate the class ID based on the IP
+	ipParts := strings.Split(ip, ".")
+	if len(ipParts) != 4 {
+		return fmt.Errorf("invalid IPv4 address: %s", ip)
+	}
+	lastOctet := ipParts[3]
+	classID := fmt.Sprintf("1:%s", lastOctet)
+
+	// Remove filters for this IP
+	// List all filters to find the ones for this class
+	cmd := exec.Command("tc", "filter", "show", "dev", interfaceName, "parent", "1:")
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		logger.Warn("Failed to list filters for peer IP %s: %v, output: %s", ip, err, string(output))
+	} else {
+		// Parse the output to find filter handles that match this classID
+		// The output format includes lines like:
+		// filter parent 1: protocol ip pref 1 u32 chain 0 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:4
+		lines := strings.Split(string(output), "\n")
+		for _, line := range lines {
+			// Look for lines containing our flowid (classID)
+			if strings.Contains(line, "flowid "+classID) && strings.Contains(line, "fh ") {
+				// Extract handle (format: fh 800::800)
+				parts := strings.Fields(line)
+				var handle string
+				for j, part := range parts {
+					if part == "fh" && j+1 < len(parts) {
+						handle = parts[j+1]
+						break
+					}
+				}
+				if handle != "" {
+					// Delete this filter using the handle
+					delCmd := exec.Command("tc", "filter", "del", "dev", interfaceName, "parent", "1:", "handle", handle, "prio", "1", "u32")
+					if delOutput, delErr := delCmd.CombinedOutput(); delErr != nil {
+						logger.Debug("Failed to delete filter handle %s for peer IP %s: %v, output: %s", handle, ip, delErr, string(delOutput))
+					} else {
+						logger.Debug("Deleted filter handle %s for peer IP %s", handle, ip)
+					}
+				}
+			}
+		}
+	}
+
+	// Remove the egress class on wg0
+	cmd = exec.Command("tc", "class", "del", "dev", interfaceName, "classid", classID)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		if !strings.Contains(string(output), "No such file or directory") && !strings.Contains(string(output), "Cannot find") {
+			logger.Warn("Failed to remove egress class for peer IP %s: %v, output: %s", ip, err, string(output))
+		}
+	}
+
+	// Remove the ingress class and filters on the IFB device
+	ifbClassID := fmt.Sprintf("2:%s", lastOctet)
+
+	// Check if the ifb kernel module is loaded (works inside containers too)
+	if _, err := os.Stat("/sys/module/ifb"); os.IsNotExist(err) {
+		logger.Warn("IFB module not loaded, skipping IFB setup and ingress traffic shaping")
+		logger.Info("Removed bandwidth limit for peer IP %s (egress class %s, ingress class %s)", ip, classID, ifbClassID)
+		return nil
+	}
+
+	cmd = exec.Command("tc", "filter", "show", "dev", ifbName, "parent", "2:")
+	output, err = cmd.CombinedOutput()
+	if err != nil {
+		logger.Warn("Failed to list IFB filters for peer IP %s: %v, output: %s", ip, err, string(output))
+	} else {
+		lines := strings.Split(string(output), "\n")
+		for _, line := range lines {
+			if strings.Contains(line, "flowid "+ifbClassID) && strings.Contains(line, "fh ") {
+				parts := strings.Fields(line)
+				var handle string
+				for j, part := range parts {
+					if part == "fh" && j+1 < len(parts) {
+						handle = parts[j+1]
+						break
+					}
+				}
+				if handle != "" {
+					delCmd := exec.Command("tc", "filter", "del", "dev", ifbName, "parent", "2:", "handle", handle, "prio", "1", "u32")
+					if delOutput, delErr := delCmd.CombinedOutput(); delErr != nil {
+						logger.Debug("Failed to delete IFB filter handle %s for peer IP %s: %v, output: %s", handle, ip, delErr, string(delOutput))
+					} else {
+						logger.Debug("Deleted IFB filter handle %s for peer IP %s", handle, ip)
+					}
+				}
+			}
+		}
+	}
+
+	cmd = exec.Command("tc", "class", "del", "dev", ifbName, "classid", ifbClassID)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		if !strings.Contains(string(output), "No such file or directory") && !strings.Contains(string(output), "Cannot find") {
+			logger.Warn("Failed to remove IFB class for peer IP %s: %v, output: %s", ip, err, string(output))
+		}
+	}
+
+	logger.Info("Removed bandwidth limit for peer IP %s (egress class %s, ingress class %s)", ip, classID, ifbClassID)
+	return nil
+}

proxy/proxy.go

@@ -16,6 +16,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/fosrl/gerbil/internal/metrics"
 	"github.com/fosrl/gerbil/logger"
 	"github.com/patrickmn/go-cache"
 )
@@ -69,6 +70,12 @@ type SNIProxy struct {
 
 	// Trusted upstream proxies that can send PROXY protocol
 	trustedUpstreams map[string]struct{}
+
+	// Reusable HTTP client for API requests
+	httpClient *http.Client
+
+	// Buffer pool for connection piping
+	bufferPool *sync.Pool
 }
 
 type activeTunnel struct {
@@ -374,6 +381,20 @@ func NewSNIProxy(port int, remoteConfigURL, publicKey, localProxyAddr string, lo
 		localOverrides:   overridesMap,
 		activeTunnels:    make(map[string]*activeTunnel),
 		trustedUpstreams: trustedMap,
+		httpClient: &http.Client{
+			Timeout: 5 * time.Second,
+			Transport: &http.Transport{
+				MaxIdleConns:        100,
+				MaxIdleConnsPerHost: 10,
+				IdleConnTimeout:     90 * time.Second,
+			},
+		},
+		bufferPool: &sync.Pool{
+			New: func() interface{} {
+				buf := make([]byte, 32*1024)
+				return &buf
+			},
+		},
 	}
 
 	return proxy, nil
@@ -487,6 +508,8 @@ func (p *SNIProxy) handleConnection(clientConn net.Conn) {
 	defer p.wg.Done()
 	defer clientConn.Close()
 
+	metrics.RecordSNIConnection("accepted")
+
 	logger.Debug("Accepted connection from %s", clientConn.RemoteAddr())
 
 	// Check for PROXY protocol from trusted upstream
@@ -497,10 +520,12 @@ func (p *SNIProxy) handleConnection(clientConn net.Conn) {
 		var err error
 		proxyInfo, actualClientConn, err = p.parseProxyProtocolHeader(clientConn)
 		if err != nil {
+			metrics.RecordSNIProxyProtocolParseError()
 			logger.Debug("Failed to parse PROXY protocol: %v", err)
 			return
 		}
 		if proxyInfo != nil {
+			metrics.RecordSNITrustedProxyEvent("proxy_protocol_parsed")
 			logger.Debug("Received PROXY protocol from trusted upstream: %s:%d -> %s:%d",
 				proxyInfo.SrcIP, proxyInfo.SrcPort, proxyInfo.DestIP, proxyInfo.DestPort)
 		} else {
@@ -517,11 +542,13 @@ func (p *SNIProxy) handleConnection(clientConn net.Conn) {
 	}
 
 	// Extract SNI hostname
+	clientHelloStart := time.Now()
 	hostname, clientReader, err := p.extractSNI(actualClientConn)
 	if err != nil {
 		logger.Debug("SNI extraction failed: %v", err)
 		return
 	}
+	metrics.RecordProxyTLSHandshake(hostname, time.Since(clientHelloStart).Seconds())
 
 	if hostname == "" {
 		log.Println("No SNI hostname found")
@@ -569,6 +596,8 @@ func (p *SNIProxy) handleConnection(clientConn net.Conn) {
 	defer targetConn.Close()
 
 	logger.Debug("Connected to target: %s:%d", route.TargetHost, route.TargetPort)
+	metrics.RecordActiveProxyConnection(hostname, 1)
+	defer metrics.RecordActiveProxyConnection(hostname, -1)
 
 	// Send PROXY protocol header if enabled
 	if p.proxyProtocol {
@@ -618,7 +647,7 @@ func (p *SNIProxy) handleConnection(clientConn net.Conn) {
 	}()
 
 	// Start bidirectional data transfer
-	p.pipe(actualClientConn, targetConn, clientReader)
+	p.pipe(hostname, actualClientConn, targetConn, clientReader)
 }
 
 // getRoute retrieves routing information for a hostname
@@ -626,6 +655,7 @@ func (p *SNIProxy) getRoute(hostname, clientAddr string) (*RouteRecord, error) {
 	// Check local overrides first
 	if _, isOverride := p.localOverrides[hostname]; isOverride {
 		logger.Debug("Local override matched for hostname: %s", hostname)
+		metrics.RecordProxyRouteLookup("local_override", hostname)
 		return &RouteRecord{
 			Hostname:   hostname,
 			TargetHost: p.localProxyAddr,
@@ -638,6 +668,7 @@ func (p *SNIProxy) getRoute(hostname, clientAddr string) (*RouteRecord, error) {
 	_, isLocal := p.localSNIs[hostname]
 	p.localSNIsLock.RUnlock()
 	if isLocal {
+		metrics.RecordProxyRouteLookup("local", hostname)
 		return &RouteRecord{
 			Hostname:   hostname,
 			TargetHost: p.localProxyAddr,
@@ -648,13 +679,16 @@ func (p *SNIProxy) getRoute(hostname, clientAddr string) (*RouteRecord, error) {
 	// Check cache first
 	if cached, found := p.cache.Get(hostname); found {
 		if cached == nil {
+			metrics.RecordProxyRouteLookup("cached_not_found", hostname)
 			return nil, nil // Cached negative result
 		}
 		logger.Debug("Cache hit for hostname: %s", hostname)
+		metrics.RecordProxyRouteLookup("cache_hit", hostname)
 		return cached.(*RouteRecord), nil
 	}
 
 	logger.Debug("Cache miss for hostname: %s, querying API", hostname)
+	metrics.RecordProxyRouteLookup("cache_miss", hostname)
 
 	// Query API with timeout
 	ctx, cancel := context.WithTimeout(p.ctx, 5*time.Second)
@@ -682,22 +716,28 @@ func (p *SNIProxy) getRoute(hostname, clientAddr string) (*RouteRecord, error) {
 	req.Header.Set("Content-Type", "application/json")
 
 	// Make HTTP request
-	client := &http.Client{Timeout: 5 * time.Second}
+	apiStart := time.Now()
-	resp, err := client.Do(req)
+	// Make HTTP request using reusable client
+	resp, err := p.httpClient.Do(req)
 	if err != nil {
+		metrics.RecordSNIRouteAPIRequest("error")
 		return nil, fmt.Errorf("API request failed: %w", err)
 	}
 	defer resp.Body.Close()
+	metrics.RecordSNIRouteAPILatency(time.Since(apiStart).Seconds())
 
 	if resp.StatusCode == http.StatusNotFound {
+		metrics.RecordSNIRouteAPIRequest("not_found")
 		// Cache negative result for shorter time (1 minute)
 		p.cache.Set(hostname, nil, 1*time.Minute)
 		return nil, nil
 	}
 
 	if resp.StatusCode != http.StatusOK {
+		metrics.RecordSNIRouteAPIRequest("error")
 		return nil, fmt.Errorf("API returned status %d", resp.StatusCode)
 	}
+	metrics.RecordSNIRouteAPIRequest("success")
 
 	// Parse response
 	var apiResponse RouteAPIResponse
@@ -754,7 +794,7 @@ func (p *SNIProxy) selectStickyEndpoint(clientAddr string, endpoints []string) s
 }
 
 // pipe handles bidirectional data transfer between connections
-func (p *SNIProxy) pipe(clientConn, targetConn net.Conn, clientReader io.Reader) {
+func (p *SNIProxy) pipe(hostname string, clientConn, targetConn net.Conn, clientReader io.Reader) {
 	var wg sync.WaitGroup
 	wg.Add(2)
 
@@ -773,9 +813,16 @@ func (p *SNIProxy) pipe(clientConn, targetConn net.Conn, clientReader io.Reader)
 		defer wg.Done()
 		defer closeConns()
 
-		// Use a large buffer for better performance
+		// Get buffer from pool and return when done
-		buf := make([]byte, 32*1024)
+		bufPtr := p.bufferPool.Get().(*[]byte)
-		_, err := io.CopyBuffer(targetConn, clientReader, buf)
+		defer func() {
+			// Clear buffer before returning to pool to prevent data leakage
+			clear(*bufPtr)
+			p.bufferPool.Put(bufPtr)
+		}()
+
+		bytesCopied, err := io.CopyBuffer(targetConn, clientReader, *bufPtr)
+		metrics.RecordProxyBytesTransmitted(hostname, "client_to_target", bytesCopied)
 		if err != nil && err != io.EOF {
 			logger.Debug("Copy client->target error: %v", err)
 		}
@@ -786,9 +833,16 @@ func (p *SNIProxy) pipe(clientConn, targetConn net.Conn, clientReader io.Reader)
 		defer wg.Done()
 		defer closeConns()
 
-		// Use a large buffer for better performance
+		// Get buffer from pool and return when done
-		buf := make([]byte, 32*1024)
+		bufPtr := p.bufferPool.Get().(*[]byte)
-		_, err := io.CopyBuffer(clientConn, targetConn, buf)
+		defer func() {
+			// Clear buffer before returning to pool to prevent data leakage
+			clear(*bufPtr)
+			p.bufferPool.Put(bufPtr)
+		}()
+
+		bytesCopied, err := io.CopyBuffer(clientConn, targetConn, *bufPtr)
+		metrics.RecordProxyBytesTransmitted(hostname, "target_to_client", bytesCopied)
 		if err != nil && err != io.EOF {
 			logger.Debug("Copy target->client error: %v", err)
 		}

relay/relay.go

@@ -9,15 +9,19 @@ import (
 	"io"
 	"net"
 	"net/http"
+	"runtime"
 	"sync"
 	"time"
 
+	"github.com/fosrl/gerbil/internal/metrics"
 	"github.com/fosrl/gerbil/logger"
 	"golang.org/x/crypto/chacha20poly1305"
 	"golang.org/x/crypto/curve25519"
 	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
 )
 
+const relayIfname = "relay"
+
 type EncryptedHolePunchMessage struct {
 	EphemeralPublicKey string `json:"ephemeralPublicKey"`
 	Nonce              []byte `json:"nonce"`
@@ -118,6 +122,13 @@ type Packet struct {
 	n          int
 }
 
+// holePunchRateLimitEntry tracks hole punch message counts within a sliding 1-second window.
+type holePunchRateLimitEntry struct {
+	mu          sync.Mutex
+	count       int
+	windowStart time.Time
+}
+
 // WireGuard message types
 const (
 	WireGuardMessageTypeHandshakeInitiation = 1
@@ -150,9 +161,17 @@ type UDPProxyServer struct {
 	// Session tracking for WireGuard peers
 	// Key format: "senderIndex:receiverIndex"
 	wgSessions sync.Map
+	// Session index for O(1) lookup by receiver index
+	// Key: receiverIndex (uint32), Value: *WireGuardSession
+	sessionsByReceiverIndex sync.Map
 	// Communication pattern tracking for rebuilding sessions
 	// Key format: "clientIP:clientPort-destIP:destPort"
 	commPatterns sync.Map
+	// Rate limiter for encrypted hole punch messages, keyed by "ip:port"
+	holePunchRateLimiter sync.Map
+	// Cache for resolved UDP addresses to avoid per-packet DNS lookups
+	// Key: "ip:port" string, Value: *net.UDPAddr
+	addrCache sync.Map
 	// ReachableAt is the URL where this server can be reached
 	ReachableAt string
 }
@@ -164,7 +183,7 @@ func NewUDPProxyServer(parentCtx context.Context, addr, serverURL string, privat
 		addr:        addr,
 		serverURL:   serverURL,
 		privateKey:  privateKey,
-		packetChan:  make(chan Packet, 1000),
+		packetChan:  make(chan Packet, 50000), // Increased from 1000 to handle high throughput
 		ReachableAt: reachableAt,
 		ctx:         ctx,
 		cancel:      cancel,
@@ -189,8 +208,13 @@ func (s *UDPProxyServer) Start() error {
 	s.conn = conn
 	logger.Info("UDP server listening on %s", s.addr)
 
-	// Start a fixed number of worker goroutines.
+	// Start worker goroutines based on CPU cores for better parallelism
-	workerCount := 10 // TODO: Make this configurable or pick it better!
+	// At high throughput (160+ Mbps), we need many workers to avoid bottlenecks
+	workerCount := runtime.NumCPU() * 10
+	if workerCount < 20 {
+		workerCount = 20 // Minimum 20 workers
+	}
+	logger.Info("Starting %d packet workers (CPUs: %d)", workerCount, runtime.NumCPU())
 	for i := 0; i < workerCount; i++ {
 		go s.packetWorker()
 	}
@@ -210,6 +234,9 @@ func (s *UDPProxyServer) Start() error {
 	// Start the communication pattern cleanup routine
 	go s.cleanupIdleCommunicationPatterns()
 
+	// Start the hole punch rate limiter cleanup routine
+	go s.cleanupHolePunchRateLimiter()
+
 	return nil
 }
 
@@ -269,13 +296,40 @@ func (s *UDPProxyServer) packetWorker() {
 	for packet := range s.packetChan {
 		// Determine packet type by inspecting the first byte.
 		if packet.n > 0 && packet.data[0] >= 1 && packet.data[0] <= 4 {
+			metrics.RecordUDPPacket(relayIfname, "wireguard", "in")
+			metrics.RecordUDPPacketSize(relayIfname, "wireguard", float64(packet.n))
 			// Process as a WireGuard packet.
 			s.handleWireGuardPacket(packet.data, packet.remoteAddr)
 		} else {
+			metrics.RecordUDPPacket(relayIfname, "hole_punch", "in")
+			metrics.RecordUDPPacketSize(relayIfname, "hole_punch", float64(packet.n))
+			// Rate limit: allow at most 2 hole punch messages per IP:Port per second
+			rateLimitKey := packet.remoteAddr.String()
+			entryVal, _ := s.holePunchRateLimiter.LoadOrStore(rateLimitKey, &holePunchRateLimitEntry{
+				windowStart: time.Now(),
+			})
+			rlEntry := entryVal.(*holePunchRateLimitEntry)
+			rlEntry.mu.Lock()
+			now := time.Now()
+			if now.Sub(rlEntry.windowStart) >= time.Second {
+				rlEntry.count = 0
+				rlEntry.windowStart = now
+			}
+			rlEntry.count++
+			allowed := rlEntry.count <= 2
+			rlEntry.mu.Unlock()
+			if !allowed {
+				// logger.Debug("Rate limiting hole punch message from %s", rateLimitKey)
+				metrics.RecordHolePunchEvent(relayIfname, "rate_limited")
+				bufferPool.Put(packet.data[:1500])
+				continue
+			}
+
 			// Process as an encrypted hole punch message
 			var encMsg EncryptedHolePunchMessage
 			if err := json.Unmarshal(packet.data, &encMsg); err != nil {
 				logger.Error("Error unmarshaling encrypted message: %v", err)
+				metrics.RecordHolePunchEvent(relayIfname, "error")
 				// Return the buffer to the pool for reuse and continue with next packet
 				bufferPool.Put(packet.data[:1500])
 				continue
@@ -283,6 +337,7 @@ func (s *UDPProxyServer) packetWorker() {
 
 			if encMsg.EphemeralPublicKey == "" {
 				logger.Error("Received malformed message without ephemeral key")
+				metrics.RecordHolePunchEvent(relayIfname, "error")
 				// Return the buffer to the pool for reuse and continue with next packet
 				bufferPool.Put(packet.data[:1500])
 				continue
@@ -291,7 +346,8 @@ func (s *UDPProxyServer) packetWorker() {
 			// This appears to be an encrypted message
 			decryptedData, err := s.decryptMessage(encMsg)
 			if err != nil {
-				logger.Error("Failed to decrypt message: %v", err)
+				// logger.Error("Failed to decrypt message: %v", err)
+				metrics.RecordHolePunchEvent(relayIfname, "error")
 				// Return the buffer to the pool for reuse and continue with next packet
 				bufferPool.Put(packet.data[:1500])
 				continue
@@ -301,6 +357,7 @@ func (s *UDPProxyServer) packetWorker() {
 			var msg HolePunchMessage
 			if err := json.Unmarshal(decryptedData, &msg); err != nil {
 				logger.Error("Error unmarshaling decrypted message: %v", err)
+				metrics.RecordHolePunchEvent(relayIfname, "error")
 				// Return the buffer to the pool for reuse and continue with next packet
 				bufferPool.Put(packet.data[:1500])
 				continue
@@ -320,6 +377,7 @@ func (s *UDPProxyServer) packetWorker() {
 			logger.Debug("Created endpoint from packet remoteAddr %s: IP=%s, Port=%d", packet.remoteAddr.String(), endpoint.IP, endpoint.Port)
 			s.notifyServer(endpoint)
 			s.clearSessionsForIP(endpoint.IP) // Clear sessions for this IP to allow re-establishment
+			metrics.RecordHolePunchEvent(relayIfname, "success")
 		}
 		// Return the buffer to the pool for reuse.
 		bufferPool.Put(packet.data[:1500])
@@ -387,6 +445,8 @@ func (s *UDPProxyServer) fetchInitialMappings() error {
 		mapping.LastUsed = time.Now()
 		s.proxyMappings.Store(key, mapping)
 	}
+	metrics.RecordProxyInitialMappings(relayIfname, int64(len(initialMappings.Mappings)))
+	metrics.RecordProxyMapping(relayIfname, int64(len(initialMappings.Mappings)))
 	logger.Info("Loaded %d initial proxy mappings", len(initialMappings.Mappings))
 	return nil
 }
@@ -416,6 +476,43 @@ func extractWireGuardIndices(packet []byte) (uint32, uint32, bool) {
 	return 0, 0, false
 }
 
+// cachedAddr holds a resolved UDP address with TTL
+type cachedAddr struct {
+	addr      *net.UDPAddr
+	expiresAt time.Time
+}
+
+// addrCacheTTL is how long resolved addresses are cached before re-resolving
+const addrCacheTTL = 5 * time.Minute
+
+// getCachedAddr returns a cached UDP address or resolves and caches it.
+// This avoids per-packet DNS lookups which are a major throughput bottleneck.
+func (s *UDPProxyServer) getCachedAddr(ip string, port int) (*net.UDPAddr, error) {
+	key := fmt.Sprintf("%s:%d", ip, port)
+
+	// Check cache first
+	if cached, ok := s.addrCache.Load(key); ok {
+		entry := cached.(*cachedAddr)
+		if time.Now().Before(entry.expiresAt) {
+			return entry.addr, nil
+		}
+		// Cache expired, delete and re-resolve
+		s.addrCache.Delete(key)
+	}
+
+	// Resolve and cache
+	addr, err := net.ResolveUDPAddr("udp", key)
+	if err != nil {
+		return nil, err
+	}
+
+	s.addrCache.Store(key, &cachedAddr{
+		addr:      addr,
+		expiresAt: time.Now().Add(addrCacheTTL),
+	})
+	return addr, nil
+}
+
 // Updated to handle multi-peer WireGuard communication
 func (s *UDPProxyServer) handleWireGuardPacket(packet []byte, remoteAddr *net.UDPAddr) {
 	if len(packet) == 0 {
@@ -450,7 +547,7 @@ func (s *UDPProxyServer) handleWireGuardPacket(packet []byte, remoteAddr *net.UD
 		logger.Debug("Forwarding handshake initiation from %s (sender index: %d) to peers %v", remoteAddr, senderIndex, proxyMapping.Destinations)
 
 		for _, dest := range proxyMapping.Destinations {
-			destAddr, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", dest.DestinationIP, dest.DestinationPort))
+			destAddr, err := s.getCachedAddr(dest.DestinationIP, dest.DestinationPort)
 			if err != nil {
 				logger.Error("Failed to resolve destination address: %v", err)
 				continue
@@ -465,7 +562,11 @@ func (s *UDPProxyServer) handleWireGuardPacket(packet []byte, remoteAddr *net.UD
 			_, err = conn.Write(packet)
 			if err != nil {
 				logger.Debug("Failed to forward handshake initiation: %v", err)
+				metrics.RecordProxyConnectionError(relayIfname, "write_udp")
+				continue
 			}
+			metrics.RecordUDPPacket(relayIfname, "wireguard", "out")
+			metrics.RecordUDPPacketSize(relayIfname, "wireguard", float64(len(packet)))
 		}
 
 	case WireGuardMessageTypeHandshakeResponse:
@@ -477,16 +578,23 @@ func (s *UDPProxyServer) handleWireGuardPacket(packet []byte, remoteAddr *net.UD
 		sessionKey := fmt.Sprintf("%d:%d", receiverIndex, senderIndex)
 
 		// Store the session information
-		s.wgSessions.Store(sessionKey, &WireGuardSession{
+		session := &WireGuardSession{
 			ReceiverIndex: receiverIndex,
 			SenderIndex:   senderIndex,
 			DestAddr:      remoteAddr,
 			LastSeen:      time.Now(),
-		})
+		}
+		if _, loaded := s.wgSessions.LoadOrStore(sessionKey, session); loaded {
+			s.wgSessions.Store(sessionKey, session)
+		} else {
+			metrics.RecordSession(relayIfname, 1)
+		}
+		// Also index by sender index for O(1) lookup in transport data path
+		s.sessionsByReceiverIndex.Store(senderIndex, session)
 
 		// Forward the response to the original sender
 		for _, dest := range proxyMapping.Destinations {
-			destAddr, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", dest.DestinationIP, dest.DestinationPort))
+			destAddr, err := s.getCachedAddr(dest.DestinationIP, dest.DestinationPort)
 			if err != nil {
 				logger.Error("Failed to resolve destination address: %v", err)
 				continue
@@ -501,28 +609,26 @@ func (s *UDPProxyServer) handleWireGuardPacket(packet []byte, remoteAddr *net.UD
 			_, err = conn.Write(packet)
 			if err != nil {
 				logger.Error("Failed to forward handshake response: %v", err)
+				metrics.RecordProxyConnectionError(relayIfname, "write_udp")
+				continue
 			}
+			metrics.RecordUDPPacket(relayIfname, "wireguard", "out")
+			metrics.RecordUDPPacketSize(relayIfname, "wireguard", float64(len(packet)))
 		}
 
 	case WireGuardMessageTypeTransportData:
 		// Data packet: forward only to the established session peer
 		// logger.Debug("Received transport data with receiver index %d from %s", receiverIndex, remoteAddr)
 
-		// Look up the session based on the receiver index
+		// Look up the session based on the receiver index - O(1) lookup instead of O(n) Range
 		var destAddr *net.UDPAddr
 
-		// First check for existing sessions to see if we know where to send this packet
+		// Fast path: direct index lookup by receiver index
-		s.wgSessions.Range(func(k, v interface{}) bool {
+		if sessionObj, ok := s.sessionsByReceiverIndex.Load(receiverIndex); ok {
-			session := v.(*WireGuardSession)
+			session := sessionObj.(*WireGuardSession)
-			// Check if session matches (read lock for check)
-			if session.GetSenderIndex() == receiverIndex {
-				// Found matching session - get dest addr and update last seen
 			destAddr = session.GetDestAddr()
 			session.UpdateLastSeen()
-				return false // stop iteration
 		}
-			return true // continue iteration
-		})
 
 		if destAddr != nil {
 			// We found a specific peer to forward to
@@ -538,12 +644,16 @@ func (s *UDPProxyServer) handleWireGuardPacket(packet []byte, remoteAddr *net.UD
 			_, err = conn.Write(packet)
 			if err != nil {
 				logger.Debug("Failed to forward transport data: %v", err)
+				metrics.RecordProxyConnectionError(relayIfname, "write_udp")
+				return
 			}
+			metrics.RecordUDPPacket(relayIfname, "wireguard", "out")
+			metrics.RecordUDPPacketSize(relayIfname, "wireguard", float64(len(packet)))
 		} else {
 			// No known session, fall back to forwarding to all peers
 			logger.Debug("No session found for receiver index %d, forwarding to all destinations", receiverIndex)
 			for _, dest := range proxyMapping.Destinations {
-				destAddr, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", dest.DestinationIP, dest.DestinationPort))
+				destAddr, err := s.getCachedAddr(dest.DestinationIP, dest.DestinationPort)
 				if err != nil {
 					logger.Error("Failed to resolve destination address: %v", err)
 					continue
@@ -561,7 +671,11 @@ func (s *UDPProxyServer) handleWireGuardPacket(packet []byte, remoteAddr *net.UD
 				_, err = conn.Write(packet)
 				if err != nil {
 					logger.Debug("Failed to forward transport data: %v", err)
+					metrics.RecordProxyConnectionError(relayIfname, "write_udp")
+					continue
 				}
+				metrics.RecordUDPPacket(relayIfname, "wireguard", "out")
+				metrics.RecordUDPPacketSize(relayIfname, "wireguard", float64(len(packet)))
 			}
 		}
 
@@ -571,7 +685,7 @@ func (s *UDPProxyServer) handleWireGuardPacket(packet []byte, remoteAddr *net.UD
 
 		// Forward to all peers
 		for _, dest := range proxyMapping.Destinations {
-			destAddr, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", dest.DestinationIP, dest.DestinationPort))
+			destAddr, err := s.getCachedAddr(dest.DestinationIP, dest.DestinationPort)
 			if err != nil {
 				logger.Error("Failed to resolve destination address: %v", err)
 				continue
@@ -586,7 +700,11 @@ func (s *UDPProxyServer) handleWireGuardPacket(packet []byte, remoteAddr *net.UD
 			_, err = conn.Write(packet)
 			if err != nil {
 				logger.Error("Failed to forward WireGuard packet: %v", err)
+				metrics.RecordProxyConnectionError(relayIfname, "write_udp")
+				continue
 			}
+			metrics.RecordUDPPacket(relayIfname, "wireguard", "out")
+			metrics.RecordUDPPacketSize(relayIfname, "wireguard", float64(len(packet)))
 		}
 	}
 }
@@ -604,6 +722,7 @@ func (s *UDPProxyServer) getOrCreateConnection(destAddr *net.UDPAddr, remoteAddr
 	// Create new connection
 	newConn, err := net.DialUDP("udp", nil, destAddr)
 	if err != nil {
+		metrics.RecordProxyConnectionError(relayIfname, "dial_udp")
 		return nil, fmt.Errorf("failed to create UDP connection: %v", err)
 	}
 
@@ -627,6 +746,8 @@ func (s *UDPProxyServer) handleResponses(conn *net.UDPConn, destAddr *net.UDPAdd
 			logger.Debug("Error reading response from %s: %v", destAddr.String(), err)
 			return
 		}
+		metrics.RecordUDPPacket(relayIfname, "wireguard", "in")
+		metrics.RecordUDPPacketSize(relayIfname, "wireguard", float64(n))
 
 		// Process the response to track sessions if it's a WireGuard packet
 		if n > 0 && buffer[0] >= 1 && buffer[0] <= 4 {
@@ -634,12 +755,19 @@ func (s *UDPProxyServer) handleResponses(conn *net.UDPConn, destAddr *net.UDPAdd
 			if ok && buffer[0] == WireGuardMessageTypeHandshakeResponse {
 				// Store the session mapping for the handshake response
 				sessionKey := fmt.Sprintf("%d:%d", senderIndex, receiverIndex)
-				s.wgSessions.Store(sessionKey, &WireGuardSession{
+				session := &WireGuardSession{
 					ReceiverIndex: receiverIndex,
 					SenderIndex:   senderIndex,
 					DestAddr:      destAddr,
 					LastSeen:      time.Now(),
-				})
+				}
+				if _, loaded := s.wgSessions.LoadOrStore(sessionKey, session); loaded {
+					s.wgSessions.Store(sessionKey, session)
+				} else {
+					metrics.RecordSession(relayIfname, 1)
+				}
+				// Also index by sender index for O(1) lookup
+				s.sessionsByReceiverIndex.Store(senderIndex, session)
 				logger.Debug("Stored session mapping: %s -> %s", sessionKey, destAddr.String())
 			} else if ok && buffer[0] == WireGuardMessageTypeTransportData {
 				// Track communication pattern for session rebuilding (reverse direction)
@@ -651,7 +779,11 @@ func (s *UDPProxyServer) handleResponses(conn *net.UDPConn, destAddr *net.UDPAdd
 		_, err = s.conn.WriteToUDP(buffer[:n], remoteAddr)
 		if err != nil {
 			logger.Error("Failed to forward response: %v", err)
+			metrics.RecordProxyConnectionError(relayIfname, "write_udp")
+			continue
 		}
+		metrics.RecordUDPPacket(relayIfname, "wireguard", "out")
+		metrics.RecordUDPPacketSize(relayIfname, "wireguard", float64(n))
 	}
 }
 
@@ -662,15 +794,18 @@ func (s *UDPProxyServer) cleanupIdleConnections() {
 	for {
 		select {
 		case <-ticker.C:
+			cleanupStart := time.Now()
 			now := time.Now()
 			s.connections.Range(func(key, value interface{}) bool {
 				destConn := value.(*DestinationConn)
 				if now.Sub(destConn.lastUsed) > 10*time.Minute {
 					destConn.conn.Close()
 					s.connections.Delete(key)
+					metrics.RecordProxyCleanupRemoved(relayIfname, "conn", 1)
 				}
 				return true
 			})
+			metrics.RecordProxyIdleCleanupDuration(relayIfname, "conn", time.Since(cleanupStart).Seconds())
 		case <-s.ctx.Done():
 			return
 		}
@@ -685,16 +820,20 @@ func (s *UDPProxyServer) cleanupIdleSessions() {
 	for {
 		select {
 		case <-ticker.C:
+			cleanupStart := time.Now()
 			now := time.Now()
 			s.wgSessions.Range(func(key, value interface{}) bool {
 				session := value.(*WireGuardSession)
 				// Use thread-safe method to read LastSeen
 				if now.Sub(session.GetLastSeen()) > 15*time.Minute {
 					s.wgSessions.Delete(key)
+					metrics.RecordSession(relayIfname, -1)
+					metrics.RecordProxyCleanupRemoved(relayIfname, "session", 1)
 					logger.Debug("Removed idle session: %s", key)
 				}
 				return true
 			})
+			metrics.RecordProxyIdleCleanupDuration(relayIfname, "session", time.Since(cleanupStart).Seconds())
 		case <-s.ctx.Done():
 			return
 		}
@@ -708,16 +847,20 @@ func (s *UDPProxyServer) cleanupIdleProxyMappings() {
 	for {
 		select {
 		case <-ticker.C:
+			cleanupStart := time.Now()
 			now := time.Now()
 			s.proxyMappings.Range(func(key, value interface{}) bool {
 				mapping := value.(ProxyMapping)
 				// Remove mappings that haven't been used in 30 minutes
 				if now.Sub(mapping.LastUsed) > 30*time.Minute {
 					s.proxyMappings.Delete(key)
+					metrics.RecordProxyMapping(relayIfname, -1)
+					metrics.RecordProxyCleanupRemoved(relayIfname, "proxy_mapping", 1)
 					logger.Debug("Removed idle proxy mapping: %s", key)
 				}
 				return true
 			})
+			metrics.RecordProxyIdleCleanupDuration(relayIfname, "proxy_mapping", time.Since(cleanupStart).Seconds())
 		case <-s.ctx.Done():
 			return
 		}
@@ -760,6 +903,11 @@ func (s *UDPProxyServer) notifyServer(endpoint ClientEndpoint) {
 	key := fmt.Sprintf("%s:%d", endpoint.IP, endpoint.Port)
 	logger.Debug("About to store proxy mapping with key: %s (from endpoint IP=%s, Port=%d)", key, endpoint.IP, endpoint.Port)
 	mapping.LastUsed = time.Now()
+	if _, existed := s.proxyMappings.Load(key); existed {
+		metrics.RecordProxyMappingUpdate(relayIfname)
+	} else {
+		metrics.RecordProxyMapping(relayIfname, 1)
+	}
 	s.proxyMappings.Store(key, mapping)
 
 	logger.Debug("Stored proxy mapping for %s with %d destinations (timestamp: %v)", key, len(mapping.Destinations), mapping.LastUsed)
@@ -772,6 +920,11 @@ func (s *UDPProxyServer) UpdateProxyMapping(sourceIP string, sourcePort int, des
 		Destinations: destinations,
 		LastUsed:     time.Now(),
 	}
+	if _, existed := s.proxyMappings.Load(key); existed {
+		metrics.RecordProxyMappingUpdate(relayIfname)
+	} else {
+		metrics.RecordProxyMapping(relayIfname, 1)
+	}
 	s.proxyMappings.Store(key, mapping)
 }
 
@@ -838,6 +991,10 @@ func (s *UDPProxyServer) clearSessionsForIP(ip string) {
 	for _, key := range keysToDelete {
 		s.wgSessions.Delete(key)
 	}
+	if len(keysToDelete) > 0 {
+		metrics.RecordSession(relayIfname, -int64(len(keysToDelete)))
+		metrics.RecordProxyCleanupRemoved(relayIfname, "session", int64(len(keysToDelete)))
+	}
 
 	logger.Debug("Cleared %d sessions for WG IP: %s", len(keysToDelete), ip)
 }
@@ -998,7 +1155,9 @@ func (s *UDPProxyServer) trackCommunicationPattern(fromAddr, toAddr *net.UDPAddr
 			pattern.LastFromDest = now
 		}
 
-		s.commPatterns.Store(patternKey, pattern)
+		if _, loaded := s.commPatterns.LoadOrStore(patternKey, pattern); !loaded {
+			metrics.RecordCommPattern(relayIfname, 1)
+		}
 	}
 }
 
@@ -1016,26 +1175,55 @@ func (s *UDPProxyServer) tryRebuildSession(pattern *CommunicationPattern) {
 		sessionKey := fmt.Sprintf("%d:%d", pattern.DestIndex, pattern.ClientIndex)
 
 		// Check if we already have this session
-		if _, exists := s.wgSessions.Load(sessionKey); !exists {
+		session := &WireGuardSession{
-			s.wgSessions.Store(sessionKey, &WireGuardSession{
 			ReceiverIndex: pattern.DestIndex,
 			SenderIndex:   pattern.ClientIndex,
 			DestAddr:      pattern.ToDestination,
 			LastSeen:      time.Now(),
-			})
+		}
+		if _, loaded := s.wgSessions.LoadOrStore(sessionKey, session); loaded {
+			s.wgSessions.Store(sessionKey, session)
+		} else {
+			metrics.RecordSession(relayIfname, 1)
+			metrics.RecordSessionRebuilt(relayIfname)
+		}
 		logger.Info("Rebuilt WireGuard session from communication pattern: %s -> %s (packets: %d)",
 			sessionKey, pattern.ToDestination.String(), pattern.PacketCount)
 	}
-	}
 }
 
 // cleanupIdleCommunicationPatterns periodically removes idle communication patterns
+// cleanupHolePunchRateLimiter periodically evicts stale rate limit entries to prevent unbounded growth.
+func (s *UDPProxyServer) cleanupHolePunchRateLimiter() {
+	ticker := time.NewTicker(30 * time.Second)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ticker.C:
+			now := time.Now()
+			s.holePunchRateLimiter.Range(func(key, value interface{}) bool {
+				rlEntry := value.(*holePunchRateLimitEntry)
+				rlEntry.mu.Lock()
+				stale := now.Sub(rlEntry.windowStart) > 10*time.Second
+				rlEntry.mu.Unlock()
+				if stale {
+					s.holePunchRateLimiter.Delete(key)
+				}
+				return true
+			})
+		case <-s.ctx.Done():
+			return
+		}
+	}
+}
+
 func (s *UDPProxyServer) cleanupIdleCommunicationPatterns() {
 	ticker := time.NewTicker(10 * time.Minute)
 	defer ticker.Stop()
 	for {
 		select {
 		case <-ticker.C:
+			cleanupStart := time.Now()
 			now := time.Now()
 			s.commPatterns.Range(func(key, value interface{}) bool {
 				pattern := value.(*CommunicationPattern)
@@ -1049,10 +1237,13 @@ func (s *UDPProxyServer) cleanupIdleCommunicationPatterns() {
 				// Remove patterns that haven't had activity in 20 minutes
 				if now.Sub(lastActivity) > 20*time.Minute {
 					s.commPatterns.Delete(key)
+					metrics.RecordCommPattern(relayIfname, -1)
+					metrics.RecordProxyCleanupRemoved(relayIfname, "comm_pattern", 1)
 					logger.Debug("Removed idle communication pattern: %s", key)
 				}
 				return true
 			})
+			metrics.RecordProxyIdleCleanupDuration(relayIfname, "comm_pattern", time.Since(cleanupStart).Seconds())
 		case <-s.ctx.Done():
 			return
 		}