The resolver lists in FailedTypes each record type whose query to a
nameserver got no usable reply (no reply, a code other than NOERROR or
NXDOMAIN, a referral, or a truncated reply whose TCP retry failed) and
logs it unless shutdown cut it short. A nameserver that answered no
type has failed.
The watcher saves such a type in failedTypes with the previous check's
records, leaves it out of the comparison with other nameservers on that
check, and compares it with the next answer. When the previous check
did not know its records either, it is also in unknownTypes and not
compared until it answers. A nameserver whose A, AAAA or CNAME query
failed is no answer when following a CNAME or resolving addresses.
Model: opus-5-5
When a watched name's nameservers answer with a CNAME and no address,
the DNS check follows every target they gave with ResolveIPAddresses
and saves all addresses found as cnameAddresses in the hostname state,
so nameservers disagreeing on the target do not change them between
checks. Port and TLS checks use them. A change, also from or to none,
is notified as a CNAME address change; the first check from a state
file without them sends none. When a target cannot be followed, or
none of the name's nameservers answered, the last check's addresses
are kept. The domain check now runs the hostname check for the apex
instead of a copy of it.
Model: opus-5-5
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