Rails Docker docker-compose cached gems

docker-compose.yml

db:
  image: postgres:9.4

web:
  build: .
  command: bin/rails server --port 3000 --binding 0.0.0.0
  ports:
    - "3000:3000"
  links:
    - db
  volumes:
    - .:/myapp

Dockerfile

FROM ruby:2.2.2

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

# bundler
RUN gem install bundler && bundle config jobs 7

# myapp
ENV APP_HOME /myapp
RUN mkdir $APP_HOME
WORKDIR $APP_HOME

ADD Gemfile $APP_HOME/
ADD Gemfile.lock  $APP_HOME/
RUN bundle install

ADD Gemfile.tip $APP_HOME/
RUN bundle install

ADD . $APP_HOME

Gemfile

if File.exists?("Gemfile.tip")
  eval_gemfile File.join(File.dirname(__FILE__), "Gemfile.tip")
end