What I've learned by Dockerise a Rails app

First thing was to Dockerise an Erlang pub/sub server. The problem is that application can only be started in console or daemon mode. So let's use some shell tricks to wait daemon.

start # start daemon
child=$! # keep the pid in child variable
wait ${child} # wait daemon process finish

• https://en.wikipedia.org/wiki/Wait_(command)

The application also need to have database ready on boot. This is not possible with docker because the containers are just started without dependency. However, there is a trick with links by using docker-wait.

mongodbready:
  image: aanand/wait
  links:
    - mongodb

app:
  image: app
  links:
    - mongodbready
    - mongodb

• https://github.com/aanand/docker-wait

Dockerfile ADD instruction handle URL with cache support. It's useful when you have to get a source tarball.

• https://docs.docker.com/engine/reference/builder/#add

docker-compose can handle env files like dotenv project, and pretty useful when you have a Rails container and a sidekiq container that shares the same environment.

• https://docs.docker.com/compose/compose-file/#env_file (documentation is not fixed yet, but will be soon)