title: Docker, can you cache apt-get package installs?
body: <p>The beginning of my docker file is below, I change the stuff after it often but never this part, but it takes a while to run, especially <code>RUN apt-get -y install npm</code>, can I cache the package download somehow? I looked at docker caching but I don't think that is what it does?</p>
  <pre><code>FROM ubuntu:20.04
  
  RUN apt-get -y update
  RUN apt-get -y install ruby
  RUN apt-get -y install ruby-dev
  RUN apt-get -y install gcc
  RUN apt-get -y install make
  RUN gem install compass
  RUN apt-get -y install nodejs
  RUN apt-get -y install npm
  RUN apt-get -y install git
  </code></pre>