When Docker containers restart, they can get new IPs on the bridge
network. HAProxy caches DNS at config load time, so stale IPs cause
503s until config is regenerated.
Added a 'docker_dns' resolvers section pointing to Docker's embedded
DNS (127.0.0.11) with 10s hold time. Backend servers now use
'resolvers docker_dns init-addr last,libc,none' so HAProxy:
- Re-resolves container names every 10 seconds
- Falls back to last known IP if DNS is temporarily unavailable
- Starts even if a backend can't be resolved yet (init-addr none)
This eliminates 503s from container restarts, scaling, and recreation
without requiring a HAProxy config regeneration.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Josh Knapp
5ebc3fb8e8