Getting started with Fig and Rails
We're going to use Fig to set up and run a Rails/PostgreSQL app. Before starting, you'll need to have Fig installed.
Let's set up the three files that'll get us started. First, our app is going to be running inside a Docker container which contains all of its dependencies. We can define what goes inside that Docker container using a file called
Dockerfile. It'll contain this to start with:
FROM ruby RUN apt-get update -qq && apt-get install -y build-essential libpq-dev RUN mkdir /myapp WORKDIR /myapp ADD Gemfile /myapp/Gemfile RUN bundle install ADD . /myapp
Next, we have a bootstrap
Gemfile which just loads Rails. It'll be overwritten in a moment by
source 'https://rubygems.org' gem 'rails', '4.0.2'
fig.yml is where the magic happens. It describes what services our app comprises (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 we need to link them together and expose the web app's port.
db: image: postgres ports: - "5432" web: build: . command: bundle exec rackup -p 3000 volumes: - .:/myapp ports: - "3000:3000" links: - db
With those files in place, we can now generate the Rails skeleton app using
$ fig run web rails new . --force --database=postgresql --skip-bundle
First, Fig 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 a fresh app generated:
$ ls Dockerfile app fig.yml tmp Gemfile bin lib vendor Gemfile.lock config log README.rdoc config.ru public Rakefile db test
Uncomment the line in your new
Gemfile which loads
gem 'therubyracer', platforms: :ruby
Now that we've got a new
Gemfile, we need to build the image again. (This, and changes to the Dockerfile itself, should be the only times you'll need to rebuild).
$ fig build
The app is now bootable, but we're not quite there yet. By default, Rails expects a database to be running on
localhost - we need to point it at the
db container instead. We also need to change the database and username to align with the defaults set by the
Open up your newly-generated
database.yml. Replace its contents with the following:
development: &default adapter: postgresql encoding: unicode database: postgres pool: 5 username: postgres password: host: db test: <<: *default database: myapp_test
We can now boot the app.
$ fig 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 2.0.0 (2013-11-22) [x86_64-linux-gnu] myapp_web_1 | [2014-01-17 17:16:29] INFO WEBrick::HTTPServer#start: pid=1 port=3000
Finally, we just need to create the database. In another terminal, run:
$ fig run web rake db:create
And we're rolling—your app should now be running on port 3000 on your docker daemon (if you're using boot2docker,
boot2docker ip will tell you its address).