Simple Ruby on Rails Dockerfile - https://docs.google.com/presentation/d/1-zbeD9s1LrVjGWqASR47JzMuNGdWoBdsF4c7QZIaA-E/edit#slide=id.p

Dockerfile

FROM ruby:2.5 

WORKDIR /app
RUN apt-get update && apt-get install -y build-essential nodejs

COPY Gemfile Gemfile.lock ./ 
RUN gem install bundler && bundle install

COPY . ./

EXPOSE 3000

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