[dnsdist] Explanation for "drops" in "showServers()"?

[Remi Gacogne]

Hi Tom,

On 6/10/21 8:03 AM, Tom via dnsdist wrote:
> In the case above, I see 14926 drops from backend01. According the 
> documentation, the backend server discards these requests. Is there a 
> way in dnsdist, to see which queries where dropped? What can cause a 
> backend server to drop requests? For example timeouts while doing name 
> resolution? Does "drops" mean that dnsdist has not received a response 
> back from the backendserver within a certain time (e.g. > setUDPTimeout)?

"Drops" values are indeed the number of queries for which dnsdist did 
not a response before the setUDPTimeout value. You can see if there was 
any recent "drops" by looking at the in-memory ring buffers storing a 
summary of the last queries and responses. For that you need to connect 
to the dnsdist console and issue a 'grepq("1000ms")' command. It will 
display queries and responses that took more than 1000ms, so the "drops" 
should be there with "T.O" in the response time column.

As for why the backend is not responding fast enough, or at all, to 
these queries, that needs to be investigated on the backend itself.

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