Dockerfile
FROM ruby:2.3.1
RUN apt-get update -qq && apt-get install -y build-essential
# for postgres
RUN apt-get install -y libpq-dev
# for nokogiri
RUN apt-get install -y libxml2-dev libxslt1-dev
# for a JS runtime
RUN apt-get install -y nodejs
ENV APP_HOME /opt/www/
RUN mkdir -p $APP_HOME
WORKDIR $APP_HOME
ADD Gemfile* $APP_HOME/
RUN bundle install
ADD . $APP_HOME