Log failures at INFO level

[xnoreq]

Hey,
currently, except for starting and stopping, almost all log messages seem to be at level DEBUG or higher.

This is fine for the initial setup and testing, as log level can easily be turned up for that, but during normal operation this would result in a lot of log spam and leaking a lot of information (query, client info) into system logs.

Could you add some messages that help in monitoring normal operation?
For example, I'd find it very helpful to see Fail-Rotate and Fail-Back groups to log when failing over to another server.
Something like:

time=... level=INFO msg="failing over to resolver" details.from=myresolver1 details.error="unexpected status code 404" details.id=myfailback1 details.resolver=myresolver2

[folbricht]

That makes sense. I'm thinking that DEBUG should still contain queries and all details, with INFO reporting on normal operations like failover etc, but no queries at all ideally not emit a log line for every query either.

I don't have access to my dev machine at the moment, at least until mid Jan. Can look at it then, or feel free to submit PRs for it.