[Pdns-users] troubleshooting dnsdist -> recursor instability

[Remi Gacogne]

Hi Christoph,

On 24/10/2022 01:46, Christoph via Pdns-users wrote:
> Is this unexpected or not unusual?
> If unusual: what would be the usual ways to further track this issue down?

Clearly unexpected. You might be able to get more information about what 
is going by setting setVerboseHealthChecks [1] in dnsdist. Otherwise you 
might have to look at the metrics reported by the recursor, or capture 
the traffic (look for UDP queries for a.root-servers.net type A).

One unrelated thing I noticed in your configuration is that you are 
setting maxInFlight to 1000 on newServer, telling dnsdist to send up to 
1000 concurrent queries on an outgoing TCP connection to the backend, 
but on the recursor's side it looks like 
max-concurrent-requests-per-tcp-connection [2] is set to the default of 
10. This might lead to terrible latency numbers over TCP, so I would 
suggest increasing that setting, or decreasing the maxInFlight value in 
the dnsdist configuration.


[1]: https://dnsdist.org/reference/config.html#setVerboseHealthChecks
[2]: 
https://docs.powerdns.com/recursor/settings.html#max-concurrent-requests-per-tcp-connection

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

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