Performance of KVS in dnsdist

Hello everyone,


I have a discussion with some of our developers about the experimental 
feature KVS in dnsdist.


We use dnsdist in front of PowerDNS (with MySQL) backends. With KVS we 
could check if a domain or record exists before we forward the request 
to PowerDNS.


Changes in our zones or database will happen quite often, I think that 
we have changes every minute. We have appr. 300k zones with >3 million 
records in our database.


One idea is to use KVS with CDB files just in case of an attack, e.g. 
use the KVS lookup in combination with MaxQPSRule. The other idea is to 
create new a CDB file everytime when a change of a zone happens or a new 
zone was added.

In the first case we would generate CDB files every 15 or 30 minutes. In 
case of an attack perhaps some new zones or new records would fail to 
resolve. We would use a refreshDelay with 300 seconds.

In the later case dnsdist has to reload the CDB file quite often, we 
would set refreshDelay to 1 second. Even if we would just generate the 
CDB file e.g. once a minute, dnsdist would have to reload it every minute.


As dnsdist was made for forwarding DNS requests and not for reading CDB 
files, my fear is that dnsdist will loose performance when we reload the 
CDB file that often.


Does anyone have experience with the KVS feature and what are your 
recommendations?

Thanks for any input.


Best regards,

Oliver