Fully-working Dockerfile for a Rails app

Dockerfile

FROM ruby:2.1

RUN apt-get update && apt-get install -y nodejs

RUN mkdir -p /usr/src/app
RUN useradd -d /usr/src/app -m app
RUN chown -R app /usr/src/app
RUN chown -R app /usr/local/bundle

USER root
WORKDIR /usr/src/app
COPY Gemfile ./Gemfile
COPY Gemfile.lock ./Gemfile.lock
RUN chown -R app.app .

USER app
RUN bundle install

USER root
COPY . /usr/src/app
RUN chown -R app.app .

USER app
RUN RAILS_ENV=production bundle exec rake assets:precompile --trace

CMD ["rails","server","-b","0.0.0.0"]

This correctly handles both production and development mode, in that in development mode you would mount your local copy of the code with:

docker build -t openproject:dev .
docker run -it -v $(pwd):/usr/src/app openproject:dev

The precompiled assets in public/assets would thus be erased, and subsequent bundle install would reuse the ones already installed in /usr/local/bundle.