# 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

```json
{
  "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**

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

Dry-run first:
```bash
ansible-playbook -i hosts.ini playbooks/configure_docker_logging.yml --check
```

Single host:
```bash
ansible-playbook -i hosts.ini playbooks/configure_docker_logging.yml -e "host_target=homelab"
```

The playbook:
1. Reads existing `daemon.json` (preserves existing keys)
2. Merges in the log config
3. Validates JSON
4. Restarts the Docker daemon
5. 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:

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

Or verify a specific container has the limit:
```bash
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:
```bash
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

```bash
# 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