This repo contains simple boilerplate files that can be added to any Phoenix application so you may run it and its database inside Docker containers using Docker Compose.

• One-line dev environment setup: docker-compose up. This command creates the database, does the Dialyzer pre-work (if the project has Dialyxer installed), and everything else.
• Developer-friendly setup: Source code is mounted so that changes in the container appear on the host and vice-versa.
• Fast re-builds because the Dockerfile is written to help Docker cache the images.
• Syncing with Postgres startup delay.
• All the crappy little dependencies installed.
• No weird hacks.

Uses Elixir 1.9.4 (compatible with Phoenix 1.4), and latest Postgres.

1. Copy the three files (Dockerfile, docker-compose.yml, and run.sh) to an existing Phoenix project which you want to Dockerize.
2. Make run.sh executable, e.g. chmod +x run.sh
3. Edit the database connection settings for the environments which will use this setup (usually dev.exs and test.exs). You can hard-code the credentials for the relevant environment(s) to reference the hostname of db, a username of postgres, and an empty password, or you can specify environment-variable overrides like the following:

# Inside config/dev.ex and/or config/test.exs
config :my_app, MyApp.Repo,
  hostname: System.get_env("DB_HOST", "localhost"),
  password: System.get_env("DB_PASS", "postgres"),
  # ... etc...

4. Spin it up with docker-compose up.

Tests can be run in the container like so:

docker-compose run web mix test

Or, for a slightly faster startup time,

docker-compose exec web mix test

... I haven't found a disadvantage of re-using the running container this way.