Drone uses the `compose` section of the `.drone.yml` to specify supporting containers (ie service containers) that should be started and linked to your build container. The `compose` section of the `.drone.yml` is modeled after `docker-compose`:
```
compose:
[container_name:]
image: [image_name]
[options]
```
Example configuration that composes a Postgres and Redis container:
```yaml
compose:
cache:
image: redis
database:
image: postgres
environment:
- POSTGRES_USER=postgres
- POSTGRES_PASSWORD=mysecretpassword
```
## Service linking
Service containers share the same network as the build container (using `--net=<container>`). This means that you can access your service container using `localhost` or `127.0.0.1`.
## Service options
The service container configuration options:
*`image` - any valid Docker image name
*`pull` - if true, will always attempt to pull the latest image
*`environment` - list of environment variables, declared in `name=value` format
*`privileged` - if true, runs the container with extended privileges [1]
*`volumes` - list of bind mounted volumes on the host machine [1]
*`net` - sets the container [network mode](https://docs.docker.com/articles/networking/#container-networking) [1]
[1] Some build options are disabled for security reasons, including `volumes`, `privileged` and `net`. To enable these options, a system administrator must white-list your repository as trusted. This can be done via the repository settings screen.
