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Allow shorter resolver-query-timeout configuration

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There are use cases for which shorter timeout values make sense.
For example if there is a load balancer which sets RD=1 and
forwards queries to a BIND resolver which is then configured to
talk to backend servers which are not visible in the public NS set.
WIth a shorter timeout value the frontend can give back SERVFAIL
early when backends are not available and the ultimate client will
not penalize the BIND-frontend for non-response.

(cherry picked from commit 5f47c2b567)
This commit is contained in:
Aram Sargsyan
2024-06-06 09:16:57 +00:00
committed by Arаm Sаrgsyаn
parent 008bfb6249
commit 003cb48f0f
1 changed files with 24 additions and 8 deletions
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32
lib/dns/resolver.c
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@@ -173,11 +173,6 @@
#define MAX_SINGLE_QUERY_TIMEOUT 9000U
#define MAX_SINGLE_QUERY_TIMEOUT_US (MAX_SINGLE_QUERY_TIMEOUT * US_PER_MS)
/*
* We need to allow a individual query time to complete / timeout.
*/
#define MINIMUM_QUERY_TIMEOUT (MAX_SINGLE_QUERY_TIMEOUT + 1000U)
/*
* The default maximum number of validations and validation failures per-fetch
*/
@@ -188,9 +183,24 @@
#define DEFAULT_MAX_VALIDATION_FAILURES 1
#endif
/* The default time in seconds for the whole query to live. */
/*
* A minumum sane timeout value for the whole query to live when e.g. talking to
* a backend server and a quick timeout is preferred by the user.
*
* IMPORTANT: if changing this value, note there is a documented behavior when
* values of 'resolver-query-timeout' less than or equal to 300 are treated as
* seconds and converted to milliseconds before applying the limits, that's
* why the value of 301 was chosen as the absolute minimum in order to not break
* backward compatibility.
*/
#define MINIMUM_QUERY_TIMEOUT 301U
/*
* The default time in seconds for the whole query to live.
* We want to allow an individual query time to complete / timeout.
*/
#ifndef DEFAULT_QUERY_TIMEOUT
#define DEFAULT_QUERY_TIMEOUT MINIMUM_QUERY_TIMEOUT
#define DEFAULT_QUERY_TIMEOUT (MAX_SINGLE_QUERY_TIMEOUT + 1000U)
#endif /* ifndef DEFAULT_QUERY_TIMEOUT */
/* The maximum time in seconds for the whole query to live. */
@@ -1201,6 +1211,9 @@ fctx_cancelquery(resquery_t **queryp, isc_time_t *finish, bool no_response,
if (rtt > MAX_SINGLE_QUERY_TIMEOUT_US) {
rtt = MAX_SINGLE_QUERY_TIMEOUT_US;
}
if (rtt > fctx->res->query_timeout * US_PER_MS) {
rtt = fctx->res->query_timeout * US_PER_MS;
}
/*
* Replace the current RTT with our value.
@@ -1861,6 +1874,9 @@ fctx_setretryinterval(fetchctx_t *fctx, unsigned int rtt) {
if (us > MAX_SINGLE_QUERY_TIMEOUT_US) {
us = MAX_SINGLE_QUERY_TIMEOUT_US;
}
if (us > fctx->res->query_timeout * US_PER_MS) {
us = fctx->res->query_timeout * US_PER_MS;
}
seconds = us / US_PER_SEC;
us -= seconds * US_PER_SEC;
@@ -10861,7 +10877,7 @@ void
dns_resolver_settimeout(dns_resolver_t *resolver, unsigned int timeout) {
REQUIRE(VALID_RESOLVER(resolver));
if (timeout <= 300) {
if (timeout < MINIMUM_QUERY_TIMEOUT) {
timeout *= 1000;
}