rule: prevent rule crash from no such host error

[damnever]

The rule will crash due to alert managers restart, same with #3257 but I use dnssrv+/dnssrvnoa+.

Maybe we should make this line fault-tolerant rather than make changes in pkg/discovery/dns.

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

[damnever]

@bwplotka please take a look.

[GiedriusS]

@bwplotka please take a look.

So no one else is permitted to take a look? :(

[GiedriusS]

I think this is the right level of abstraction - it should be up to the end-user (i.e. the caller) to react in a certain way to an error. However, I don't like hardcoding the exact errors into the code at this exact place. What about having a method IsNotFoundError(err error) bool in the ipLookupResolver interface that we could use here? Then we would have same pattern as in BucketReader and I think that works well.

Then, in the case of the miekg resolver we could also return a special error if lookupWithSearchPath returns NXDOMAIN & no error so that the user of that resolver would also know when such an issue occurs.

[GiedriusS]

Just one suggestion but overall LGTM. Thank you!

[GiedriusS]

Thank you!