# Docker-Compose

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## Networking

By default Docker-Compose will create a new network for the given compose file. You can change the behavior by defining custom networks in your compose file.

### Create and assign custom network

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*Example:*

```yaml
networks:
  custom-network:

services:
  app:
    networks:
      - custom-network
```

### Use existing networks

If you want to use an existing Docker network for your compose files, you can add the `external: true` parameter in your compose file
*Example:*

```yaml
networks:
  existing-network:
    external: true
```

## Volumes

Volumes are data storage objects that Docker containers can use for persistent storage.

### Create and map static volume(s)

```yaml
volumes:
  my-volume:

services:
  app:
    volumes:
      - my-volume:/path-in-container
```

These volumes are stored in `/var/lib/docker/volumes`.

### Create volume that is a CIFS mount to external share

```yaml
# Variables that will need to be changed:  
# <PUID> - User id for folder/file permissions  
# <PGID> - Group id for folder/file permissions  
# <PATH_TO_CONFIG> - Path where Unmanic will store config files  
# <PATH_TO_ENCODE_CACHE> - Cache path for in-progress encoding tasks  
# <REMOTE_IP> - Remote IP address of CIFS mount  
# <PATH_TO_LIBRARY> - Path in remote machine to be mounted as your library  
# <USERNAME> - Remote mount username  
# <PASSWORD> - Remote mount password  
#

---  
version: '2.4'  
services:  
  app:
    container_name: app_name  
    image: repo/app:tag  
    ports:  
      - 1234:1234
    environment:  
      - PUID=<PUID>  
      - PGID=<PGID>  
    volumes:
      - cifs_mount:/path-in-container

volumes:  
  cifs_mount:  
    driver: local  
    driver_opts:  
      type: cifs  
      device: //<REMOTE_IP>/<PATH_TO_LIBRARY>  
      o: "username=<USERNAME>,password=<PASSWORD>,vers=3.0,uid=<PUID>,gid=<PGID>"
```

## Environment Variables

Environment variables can be defined in the `environment` section of a service in a Docker Compose file.

### Define environment variables

```yaml
services:
  app:
    environment:
      - ENV_VAR=value
```

### Interpolate environment variables

| Variable | Description |
| --- | --- |
| `${ENV_VAR}` | Value of `ENV_VAR` |
| `${ENV_VAR:-default}` | Value of `ENV_VAR` if set and non-empty, otherwise `default`|
| `${ENV_VAR-default}` | Value of `ENV_VAR` if set, otherwise `default`|
| `${ENV_VAR:?error}` | Value of `ENV_VAR` if set and non-empty, otherwise exit with `error` |
| `${ENV_VAR?error}` | Value of `ENV_VAR` if set, otherwise exit with `error` |
| `${ENV_VAR:+replacement}` | `replacement` if `ENV_VAR` is set and non-empty, otherwise empty |
| `${ENV_VAR+replacement}` | `replacement` if `ENV_VAR` is set, otherwise empty |