How To Test OpenRC Services with Docker-Compose

Similar to how I abused Docker conceptually to test systemd services with docker-compose, I spent some time recently trying to do the same thing with OpenRC for Alpine Linux.

It basically requires the same steps as systemd. With the base 3.12 Alpine image, it's a matter of:

1. Install OpenRC
2. Optionally map /sys/fs/cgroup
3. Start up with /sbin/init
4. Run tests via docker exec

1. Install OpenRC

The base Alpine images don't include OpenRC, so you have to install it with apk. I do this in my Dockerfile:

FROM alpine:3.12 RUN apk add openrc CMD ["/sbin/init"]

2. Optionally map /sys/fs/cgroup

Unlike with systemd, I didn't have to set up any tmpfs mounts to get OpenRC services running. I also didn't have to map the /sys/fs/cgroup directory -- but if I didn't, I would get a bunch of cgroup-related error messages when starting and stopping services (although the services themselves still seemed to work fine). So I just went ahead and mapped the dir in my docker-compose.yml to avoid those error messages:

version: '3' services: my_test_container: build: . image: my_test_image volumes: - /sys/fs/cgroup:/sys/fs/cgroup:ro

3. Start up with /sbin/init

With the Alpine openrc package, the traditional /sbin/init startup command works to start OpenRC. I added CMD ["/sbin/init"] to my Dockerfile to start up with it, but you could instead add command: /sbin/init to the service in your docker-compose.yml file.

4. Run tests via docker exec

The above docker-compose.yml and Dockerfile will allow you to start up OpenRC in my_test_container with one command:

docker-compose up -d my_test_container

With OpenRC up and running, you can use a second command to execute a shell on the very same container to test it out:

docker-compose exec my_test_container /bin/sh

Or use exec to run other commands to test the services managed by OpenRC:

docker-compose exec my_test_container rc-status --servicelist

Cleaning up

The clean up steps with OpenRC are also basically the same as with systemd:

1. Stop the running container: docker-compose stop my_test_container
2. Remove the saved container state: docker-compose rm my_test_container
3. Remove the built image: docker image rm my_test_image