So, this is a very odd situation and I'm kind of grasping at straws here.
So, I've come to see if any of you have any good straws!
The setup.
---
Ubuntu 18.04 LTS is the distro we're running on.
All software is packaged [from the distro] - not compiled from sources.
Bind9 acting as a recursive resolver for a smallish network. 150 seats.
They're also handling DHCP and Chrony/NTP requests.
[I actually have a pair of these handling DNS/DHCP/NTP this is the master.]
They are running on a Xen/XCP VM.
The one I'm having problems is the master for several internal zones - the one
that's working fine is the slave for those same zones. None of the zones are
large.
Intermittently, Bind9 simply stops handling queries from *some* hosts.
Meaning, it simply times out for responses for those hosts.
Yet BIND *is* working fine for lots of other machines on the same networks.
It's working fine doing dig queries locally on the server, and handles dns
queries fine for lots of other machines. Yet, again, some machines simply get
time-outs. I can't find any pattern to which machines get timeouts and which
don't.
I've checked - no firewalls, fail2ban or the like that might be causing this.
No selinux/apparmour.
Hosts that can't do dns queries can ping the dns server fine.
[So, there's at least some network pathway to the DNS machine.]
Review of the logs for bind don't show anything that looks like a problem to me.
[But I'm not sure what keywords I ought to be looking for, in an effort to find
symptoms/problems.]
Finally, the two bind/dhcp/ntp servers are currently running on the same Xen
host, so if it's somehow host related, I'd expect both to have problems, but
they don't.
Top doesn't show any CPU distress.
Processes look fine
Memory in use is far below what allocated to the machine. [1G allocated, like
<400M used.]
Restart of BIND doesn't do anything, at least in the cases I've seen - which
aren't all that many yet.
A restart of the whole VM does appear to fix the issue immediately.
These appear to occur every 3-5 days.
Oh, and if you simply wait, it eventually starts handling queries for all hosts
again - but it might be a couple+ hours.
Any suggestions on things I might hunt for in the logs in an attempt to figure
out what's happening?
Other suggestions for things to look for/consider?
TIA
-Greg
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