DockerComposeEnv

Simplify configuration between Docker Compose and Ruby/Rails apps in development.

If you run Rails outside of Docker, this helps your application play be a better first class citizen with your dev machine by utilizing dynamic port mapping in Docker Compose services.

To read more about the problems this gem solves, check out the Why Does This Exist? documentation.

If your team is comfortable running Rails inside a container or you are looking for a production solution for service discovery, this is not what you want.

For a Rails app, add this gem to your Gemfile in the development / test groups.

group :development, :test do
  gem 'docker_compose_env_rails'
end

You will now have new ENV properties set from the docker-compose.yml file in your project directory. The following compose config would assign ENV['DB_HOST'] and ENV['DB_PORT_5432'] to the values returned from running docker-compose port db 5432, the host and dynamically mapped port assigned after you ran docker-compose up.

version: '3.3'

services:
  db:
    image: postgres:9.6-alpine
    env_file: .env
    ports:
      - "5432"

That means your Rails config/database.yml file could look like:

default: &default
  adapter: postgresql
  encoding: unicode
  host: <%= ENV['DB_HOST'].to_i %>
  password: example
  pool: 5
  port: <%= ENV['DB_PORT_5432'].to_i %>
  username: postgres

development:
  <<: *default
  database: app

test:
  <<: *default
  database: app_test

If you need to load the dynamic port information faster than the before_configuration call in Railties, you can add the docker_compose_env gem higher up in the Gemfile and load it with a special require path:

gem `docker_compose_env`, require: 'docker_compose_env/now'

Unfortunately, there's only so much automagic that can be done. If you need to customize the docker-compose.yml file name or location, or if you'd like to collect the dynamic information somewhere besides ENV, you will need to require the docker_compose_env gem and set it up yourself.

# expects docker-compose.yml file and adds values to ENV
DockerComposeEnv.setup!

# customize docker-compose.yml path and adds values to ENV
DockerComposeEnv.setup!(file: 'docker/docker-compose.dev.yml')

# add dynamic values to custom object instead of ENV
config = {}
DockerComposeEnv.setup!(env: config)
puts config

# add dynamic values to custom object instead of ENV and custom compose path
config = {}
DockerComposeEnv.setup!(env: config, file: 'custom/path.yml')
puts config

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/CoffeeAndCode/docker_compose_env.