Dockerfile
FROM ruby:2.3.8
RUN apt-get update -qq && apt-get install -y build-essential
# for nokogiri
RUN apt-get install -y libxml2-dev libxslt1-dev
ENV APP_HOME /myapp
RUN mkdir $APP_HOME
WORKDIR $APP_HOME
ADD Gemfile* $APP_HOME/
ADD . $APP_HOME
RUN gem install bundler && bundle install