## Quickstart: Docker Compose and Rails This Quickstart guide will show you how to use Docker Compose to set up and run a Rails/PostgreSQL app. Before starting, you'll need to have [Compose installed](install.md). ### Define the project Start by setting up the three files you'll need to build the app. First, since your app is going to run inside a Docker container containing all of its dependencies, you'll need to define exactly what needs to be included in the container. This is done using a file called `Dockerfile`. To begin with, the Dockerfile consists of: FROM ruby:2.2.0 RUN apt-get update -qq && apt-get install -y build-essential libpq-dev RUN mkdir /myapp WORKDIR /myapp ADD Gemfile /myapp/Gemfile ADD Gemfile.lock /myapp/Gemfile.lock RUN bundle install ADD . /myapp That'll put your application code inside an image that will build a container with Ruby, Bundler and all your dependencies inside it. For more information on how to write Dockerfiles, see the [Docker user guide](https://docs.docker.com/engine/userguide/dockerimages/#building-an-image-from-a-dockerfile) and the [Dockerfile reference](https://docs.docker.com/engine/reference/builder/). Next, create a bootstrap `Gemfile` which just loads Rails. It'll be overwritten in a moment by `rails new`. source 'https://rubygems.org' gem 'rails', '4.2.0' You'll need an empty `Gemfile.lock` in order to build our `Dockerfile`. $ touch Gemfile.lock Finally, `docker-compose.yml` is where the magic happens. This file describes the services that comprise your app (a database and a web app), how to get each one's Docker image (the database just runs on a pre-made PostgreSQL image, and the web app is built from the current directory), and the configuration needed to link them together and expose the web app's port. version: '2' services: db: image: postgres web: build: . command: bundle exec rails s -p 3000 -b '0.0.0.0' volumes: - .:/myapp ports: - "3000:3000" depends_on: - db ### Build the project With those three files in place, you can now generate the Rails skeleton app using `docker-compose run`: $ docker-compose run web rails new . --force --database=postgresql --skip-bundle First, Compose will build the image for the `web` service using the `Dockerfile`. Then it'll run `rails new` inside a new container, using that image. Once it's done, you should have generated a fresh app: $ ls -l total 56 -rw-r--r-- 1 user staff 215 Feb 13 23:33 Dockerfile -rw-r--r-- 1 user staff 1480 Feb 13 23:43 Gemfile -rw-r--r-- 1 user staff 2535 Feb 13 23:43 Gemfile.lock -rw-r--r-- 1 root root 478 Feb 13 23:43 README.rdoc -rw-r--r-- 1 root root 249 Feb 13 23:43 Rakefile drwxr-xr-x 8 root root 272 Feb 13 23:43 app drwxr-xr-x 6 root root 204 Feb 13 23:43 bin drwxr-xr-x 11 root root 374 Feb 13 23:43 config -rw-r--r-- 1 root root 153 Feb 13 23:43 config.ru drwxr-xr-x 3 root root 102 Feb 13 23:43 db -rw-r--r-- 1 user staff 161 Feb 13 23:35 docker-compose.yml drwxr-xr-x 4 root root 136 Feb 13 23:43 lib drwxr-xr-x 3 root root 102 Feb 13 23:43 log drwxr-xr-x 7 root root 238 Feb 13 23:43 public drwxr-xr-x 9 root root 306 Feb 13 23:43 test drwxr-xr-x 3 root root 102 Feb 13 23:43 tmp drwxr-xr-x 3 root root 102 Feb 13 23:43 vendor If you are running Docker on Linux, the files `rails new` created are owned by root. This happens because the container runs as the root user. Change the ownership of the the new files. sudo chown -R $USER:$USER . If you are running Docker on Mac or Windows, you should already have ownership of all files, including those generated by `rails new`. List the files just to verify this. Uncomment the line in your new `Gemfile` which loads `therubyracer`, so you've got a Javascript runtime: gem 'therubyracer', platforms: :ruby Now that you've got a new `Gemfile`, you need to build the image again. (This, and changes to the Dockerfile itself, should be the only times you'll need to rebuild.) $ docker-compose build ### Connect the database The app is now bootable, but you're not quite there yet. By default, Rails expects a database to be running on `localhost` - so you need to point it at the `db` container instead. You also need to change the database and username to align with the defaults set by the `postgres` image. Replace the contents of `config/database.yml` with the following: development: &default adapter: postgresql encoding: unicode database: postgres pool: 5 username: postgres password: host: db test: <<: *default database: myapp_test You can now boot the app with: $ docker-compose up If all's well, you should see some PostgreSQL output, and then—after a few seconds—the familiar refrain: myapp_web_1 | [2014-01-17 17:16:29] INFO WEBrick 1.3.1 myapp_web_1 | [2014-01-17 17:16:29] INFO ruby 2.2.0 (2014-12-25) [x86_64-linux-gnu] myapp_web_1 | [2014-01-17 17:16:29] INFO WEBrick::HTTPServer#start: pid=1 port=3000 Finally, you need to create the database. In another terminal, run: $ docker-compose run web rake db:create That's it. Your app should now be running on port 3000 on your Docker daemon. If you're using [Docker Machine](https://docs.docker.com/machine/), then `docker-machine ip MACHINE_VM` returns the Docker host IP address.  >**Note**: If you stop the example application and attempt to restart it, you might get the following error: `web_1 | A server is already running. Check /myapp/tmp/pids/server.pid.` One way to resolve this is to delete the file `tmp/pids/server.pid`, and then re-start the application with `docker-compose up`. ## More Compose documentation - [User guide](index.md) - [Installing Compose](install.md) - [Getting Started](gettingstarted.md) - [Get started with Django](django.md) - [Get started with WordPress](wordpress.md) - [Command line reference](./reference/index.md) - [Compose file reference](compose-file.md)