There are two failure modes that can be expected - no target SRV DNS RRs
found or no healthy service available at target addresses. Prior to this
patch, there was no way to differentiate from log messages between the
two cases.
Introduce an EmptyCache exception which may be raised by either the
ResolverCache or HealthyCache. The exception message contains enough
information about where the exception occurred to troubleshoot issues.
An existing bug was fixed in this commit. Previously if a target address
changed during runtime, an old cached (healthy) address would be
returned.. The behaviour has been corrected to return the newly cached
address.
f38779adf4