> ## Documentation Index
> Fetch the complete documentation index at: https://www.towbar.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Container and health

> Set the app port, capacity, private network, persistent volumes, and readiness check.

The `container` block describes how the deployed image runs. `port` is the port **inside** the container; the process must listen on the container's network interface. Set resource limits near the port so a reviewer can assess expected capacity:

```yaml title=".towbar/apps/web.app.yml" theme={"system"}
container:
  port: 3000
  resources:
    cpus: 1
    memory: 1g
health:
  path: /health
  timeoutSeconds: 60
```

The HTTP health path should respond without interactive authentication. A successful build is not sufficient for traffic promotion: Towbar waits for the candidate to pass readiness. Allow enough time for startup, but investigate a consistently slow start rather than raising the timeout indefinitely.

## Private connectivity

Set the same `container.network` on an app and resource on the same server. A resource's ID is its network alias unless the resource sets `networkAlias`:

```yaml title=".towbar/apps/web.app.yml" theme={"system"}
container:
  port: 3000
  network: application
```

For a PostgreSQL resource with alias `postgres`, the app can connect to `postgres:5432`. Put the credential-bearing URL in an [app runtime secret](/docs/secrets), not in the manifest. A Docker network on one host does not connect containers across different servers.

## Persistent storage

Use a Docker-managed named volume when a process must retain files across replacement:

```yaml title=".towbar/apps/files.app.yml" theme={"system"}
rollout:
  type: recreate
  maintenanceMode: true
  reason: The app uses a single-writer volume
container:
  port: 3000
  volumes:
    - name: uploads
      mountPath: /app/uploads
      initialData: image
```

Create the mount directory in the image with ownership for its runtime user. Volumes survive redeployments and image rollback, remain on their server, and are not backed up by Towbar. `initialData` applies only when adding a new volume: `previous-container` imports from the stopped container, while `image` initializes from the new image. See the [manifest storage guide](/docs/deployment-manifest#persistent-app-storage) for missing-volume and environment behavior.