On 8/7/19 2:57 PM, Chris wrote:
> A strace and backtrace is available here:
> 
> https://gbe0.com/dnsdist/dnsdist_bt.txt.gz
> https://gbe0.com/dnsdist/dnsdist_strace.txt.gz

Thanks!
I don't see anything weird in the backtrace, no stuck threads notably.
From the strace it looks like UDP queries are being received by dnsdist
and sent to the backends, however I don't see any response coming to
dnsdist.

> When the issue occurs the metrics do not change if I send UDP queries;
> if I sent TCP queries the metrics increase as expected.

Are you sure about that? In the strace I see some of the metrics in HTTP
exchanges (you might want to change your HTTP password, by the way,
sorry about that), and it looks like the counters of received UDP
queries in the frontend do increase a bit?

I also see some healthchecks failing in the strace, sometimes with a
timeout and sometimes even with a connection refused. Several backends
in the metrics appear to be down. Is that expected?

>> It's not clear to me from your message whether going back to 1.3.x fixes
>> the issue, could you clarify that?
> 
> Sorry, I did not try 1.3.x on Debian Buster, I would need to build
> packages for that as there is a conflict that prevents installation of
> the Stretch package.

Right, we don't provide 1.3.x packages for Buster, I forgot.

I have a couple ideas to know a bit more about what's happening:
- running dnsdist in verbose mode, it will log a lot but if you can
reproduce the issue in less than a minute it might be bearable ;
- having a look at the network traffic with tcpdump, for example, to see
if the queries are forwarded to the backends and whether these respond.

I wouldn't mind having a look at your configuration either, since I can
see in the metrics that you have some rules.

Best regards,
-- 
Remi Gacogne
PowerDNS.COM BV - https://www.powerdns.com/

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