[Pdns-users] How to stop automatic respawning

Klaus Darilion klaus.darilion at nic.at
Wed Oct 6 20:28:22 UTC 2021

Hi! During random subdomain attacks we often hit the max-queue-length:

pdns_server-customer1[51284]: 5001 questions waiting for database/backend attention. Limit is 5000, respawning

This happens constantly (+50K q/s). Of course we try to filter with dnsdist/iptables/... but until our detection and dynamic filtering kicks in, the attacks fully hits PDNS and causes constant respawning. I think this respawning causes aditional load, backend DOWN/UP in dnsdist, outages during " Service hold-off time over".

When the queue is full, instead of respawning, I would like PowerDNS to:
- just stop reading from incoming sockets (Linux input buffer will overflow and packets will be dropped), or
- read packets from incoming sockets and discard them, or
- just flush the queue, or
- any other ideas?

Are there any options to avoid respawning but keep the queue-length at a sane value?


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