Docker Log Rotation

Prevents unbounded container log growth across all homelab hosts. Docker's default is no limit — a single chatty container can fill a disk.

Target Config

{
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "10m",
    "max-file": "3"
  }
}

10 MB × 3 files = max 30 MB per container.

Linux Hosts (Ansible)

Covers: homelab-vm, concord-nuc, pi-5, matrix-ubuntu

cd ansible/automation
ansible-playbook -i hosts.ini playbooks/configure_docker_logging.yml

Dry-run first:

ansible-playbook -i hosts.ini playbooks/configure_docker_logging.yml --check

Single host:

ansible-playbook -i hosts.ini playbooks/configure_docker_logging.yml -e "host_target=homelab"

The playbook:

Reads existing daemon.json (preserves existing keys)
Merges in the log config
Validates JSON
Restarts the Docker daemon
Verifies the logging driver is active

After running — recreate existing containers

The daemon default only applies to new containers. Existing ones keep their old (unlimited) config until recreated:

# On each host, per stack:
docker compose -f <compose-file> up --force-recreate -d

Or verify a specific container has the limit:

docker inspect <container> | jq '.[0].HostConfig.LogConfig'
# Should show: {"Type":"json-file","Config":{"max-file":"3","max-size":"10m"}}

Synology Hosts (Not Applicable)

atlantis, calypso, and setillo all use DSM's native db log driver (Synology Container Manager default). This driver stores container logs in an internal database managed by DSM — it does not produce json-file logs and does not support max-size/max-file options.

Do not change the log driver on Synology hosts. Switching to json-file would break the Container Manager log viewer in DSM, and the db driver already handles log retention internally.

To verify:

ssh atlantis "/var/packages/REDACTED_APP_PASSWORD/target/usr/bin/docker info 2>&1 | grep -i 'logging driver'"
# Logging Driver: db  ← expected

Guava (TrueNAS SCALE)

TrueNAS SCALE uses K3s (Kubernetes) as its primary app runtime — standard Docker daemon log limits don't apply to apps deployed through the UI. If you have standalone Docker containers on guava, apply the Linux procedure above via Ansible (truenas-scale host in inventory).

Verification

# Check largest existing logs before rotation
ssh <host> "sudo find /var/lib/docker/containers -name '*-json.log' -exec du -sh {} \; 2>/dev/null | sort -h | tail -10"

# Check a container's effective log config
docker inspect <name> | jq '.[0].HostConfig.LogConfig'

# Check daemon logging driver
docker info --format '{{.LoggingDriver}}'

What This Doesn't Do

Does not truncate existing log files — those are handled by the reactive log_rotation.yml playbook
Does not apply to containers started before the daemon restart — recreate them
Does not configure per-container overrides — individual services can still override in their compose with logging: if needed

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