Dockerfile example for a Rails app

Dockerfile

# Select ubuntu as the base image
FROM ruby:2.2.0

# see update.sh for why all "apt-get install"s have to stay as one long line
RUN apt-get update && apt-get install -y nodejs --no-install-recommends && rm -rf /var/lib/apt/lists/*

# see http://guides.rubyonrails.org/command_line.html#rails-dbconsole
RUN apt-get update && apt-get install -qy postgresql-client sqlite3 imagemagick libmagickwand-dev --no-install-recommends && rm -rf /var/lib/apt/lists/*

ENV RAILS_VERSION 4.1.1

RUN gem install rails --version "$RAILS_VERSION"

MAINTAINER Michelangelo Chasseur <michelangelo.chasseur@touchwa.re>

# Create directory from where the code will run 
RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app

# Make unicorn reachable to other containers 
EXPOSE 3000

# Set ENV variables
ENV PORT=3000

# Container should behave like a standalone executable 
CMD ["foreman","start"]

# Install the necessary gems 
ADD Gemfile /usr/src/app/Gemfile
ADD Gemfile.lock /usr/src/app/Gemfile.lock
RUN bundle install --without development test

# Add rails project (from same dir as Dockerfile) to project directory
ADD ./ /usr/src/app

# Run rake tasks
RUN RAILS_ENV=production rake db:create db:migrate