[dns-operations] some advice on configuring the dns resolver inside "systemd"

[Florian Weimer]

* Robert Edmonds:

> He also spends a lot of time complaining about "implementing state
> tracking against a stateless protocol" (he appears to think that that's
> bad), yet the recursive DNS server he recommends implements exactly that
> (https://www.unbound.net/documentation/info_timeout.html), and much more
> (e.g., RTT tracking).

It's also not true that the glibc stub resolver, when configured with
rotate/RES_ROTATE, always picks the first configured resolver for each
new process.  For a long time, it has been the *second* one, and the
bug was never fixed before the first serverchoice in a process was
made random.

The fact is that some users push very hard for state tracking in the
stub resolver because that's what they are used to from other systems,
despite its inherent limitations. It's unlikely that we're going to
implement this part of the glibc stub resolver, though, because there
already many alternative solutions.