The "mirror" system test checks whether log messages announcing a mirror
zone coming into effect are emitted properly. However, the helper
functions responsible for waiting for zone transfers and zone loading to
complete do not wait for these exact log messages, but rather for other
ones preceding them, which introduces a possibility of false positives.
This problem cannot be addressed by just changing the log message to
look for because the test still needs to discern between transferring a
zone and loading a zone.
Add two new log messages at debug level 99 (which is what named
instances used in system tests are configured with) that are to be
emitted after the log messages announcing a mirror zone coming into
effect. Tweak the aforementioned helper functions to only return once
the log messages they originally looked for are followed by the newly
added log messages. This reliably prevents races when looking for
"mirror zone is now in use" log messages and also enables a workaround
previously put into place in the "mirror" system test to be reverted.
In the "mirror" system test, ns3 periodically sends trust anchor
telemetry queries to ns1 and ns2. It may thus happen that for some
non-recursive queries for names inside mirror zones which are not yet
loaded, ns3 will be able to synthesize a negative answer from the cached
records it obtained from trust anchor telemetry responses. In such
cases, NXDOMAIN responses will be sent with the root zone SOA in the
AUTHORITY section. Since the root zone used in the "mirror" system test
has the same serial number as ns2/verify.db.in and zone verification
checks look for the specified serial numbers anywhere in the answer, the
test could be broken if different zone names were used.
The +noauth dig option could be used to address this weakness, but that
would prevent entire responses from being stored for later inspection,
which in turn would hamper troubleshooting test failures. Instead, use
a different serial number for ns2/verify.db.in than for any other zone
used in the "mirror" system test and check the number of records in the
ANSWER section of each response.
Due to the way the "mirror" system test is set up, it is impossible for
the "verify-unsigned" and "verify-untrusted" zones to contain any serial
number other than the original one present in ns2/verify.db.in. Thus,
using presence of a different serial number in the SOA records of these
zones as an indicator of problems with mirror zone verification is
wrong. Look for the original zone serial number instead as that is the
one that will be returned by ns3 if one of the aforementioned zones is
successfully verified.
Add a warning about potential performance implications of configuring a
non-root zone as a mirror zone. Explain in more detail how each mirror
zone version is validated and how validation failures are handled. Move
the paragraphs describing how to set up IANA root zone mirroring higher
up, so that they can be more easily found by the reader. Explicitly
state that the "masters" option needs to be present for any mirror zone
which is not the root zone. Tweak the description of the interaction
between the "dnssec-validation" setting and root zone mirroring to make
it less ambiguous. Specify what the default "notify" setting is for
mirror zones.
