dnsdist applies QPS to backend server even on cache hit

[ahupowerdns]

• Program: dnsdist
• Issue type: Bug report

Short description

The firstAvailable policy uses QPS limits per server. These do not work as intended if a cache is attached to a pool: we first pick a server and THEN consult the cache. This means the server selection policy sees the uncached QPS, not the cached QPS.

This not alone breaks the QPS but also causes additional work.

Environment

dnsdist from master

Steps to reproduce

Configure backends with QPS, configure a cache, send ton of cacheable traffic.