reverse-proxy runs Swarm mode:global (one instance per node), all
writing to the same CephFS file. This wrapper uses a shared flock +
shared logrotate state file (both also on the CephFS mount) so cron
on docker-1/2/3 can run independently without racing or double-rotating.
Traefik has no built-in log rotation and no SIGUSR1/reopen handling.
--accesslog.filePath and --log.filePath (traefik.yaml) write directly
to /volume1/docker/traefik/logs, which had grown to 15.5GB unrotated,
contributing to disk pressure (docker-2 CephFS at 82%) and adding
write latency to every request through Traefik.
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