# Docker

## Package policy

The profile prefers Ubuntu's `docker.io` package. If that package is
unavailable after an APT refresh, it configures Docker's official Ubuntu
repository and installs Docker Engine, containerd, Buildx, and Compose plugins.

This fallback requires network access to `download.docker.com`.

## Daemon configuration

The managed settings are:

```json
{
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "50m",
    "max-file": "5"
  }
}
```

Existing valid `/etc/docker/daemon.json` content is preserved and merged with
these log settings. A changed file is backed up with a timestamp. Invalid JSON
causes the profile to stop rather than overwrite operator configuration.

Log limits apply to newly created containers. Existing containers may retain
their original logging configuration until recreated.

## Validation

```bash
docker version
docker compose version
docker info
docker ps
docker system df
jq . /etc/docker/daemon.json
```

## Troubleshooting and rollback

```bash
systemctl status docker
journalctl -u docker
jq empty /etc/docker/daemon.json
```

To restore a previous daemon configuration, review a timestamped backup,
replace the current file, validate it with `jq empty`, and restart Docker.
Do not restore blindly when workloads depend on newer daemon settings.

The profile does not configure Docker data roots, prune objects, deploy
applications, or install the NVIDIA Container Toolkit.