Example Docker File to start a Rails app located in a local ./docker-rails directory.

Dockerfile

# docker build -t="rails" .

FROM ubuntu:12.04

RUN apt-get update

## MYSQL
RUN apt-get install -y -q mysql-client libmysqlclient-dev

## RUBY
RUN apt-get install -y -q ruby1.9.1 ruby1.9.1-dev rubygems1.9.1 irb1.9.1 build-essential libopenssl-ruby1.9.1 libssl-dev zlib1g-dev

## RAILS
RUN gem install rails --no-ri --no-rdoc

## For execjs - needs node
RUN apt-get install -y python-software-properties python python-setuptools ruby rubygems
RUN add-apt-repository ppa:chris-lea/node.js
RUN echo "deb http://us.archive.ubuntu.com/ubuntu/ precise universe" >> /etc/apt/sources.list
RUN apt-get update
RUN apt-get install -y nodejs

## RAILS APP
ADD ./docker-rails /srv/docker-rails
RUN cd /srv/docker-rails;bundle install
EXPOSE 3000

RUN easy_install supervisor
RUN echo_supervisord_conf > /etc/supervisord.conf
RUN printf "[include]\nfiles = /srv/docker-rails/Supervisorfile\n" >> /etc/supervisord.conf

CMD ["/usr/local/bin/supervisord", "-n", "-c", "/etc/supervisord.conf"]