title: Where does docker install dependencies?
body: <p>This is a beginner question but I started learning about docker and how each container is isolated from another container.</p>
  
  <p>In an example in the lesson, the video said that the great thing about docker is that we can ignore dependency conflicts so if we have <code>image A</code> that requires <code>dependency A v1.0</code> and <code>image B</code> that requires <code>dependency A v2.0</code>, then it's as simple as specifying it in the docker image and we don't have to worry about conflicts about versions and whatnot. </p>
  
  <p>Now my questions are:</p>
  
  <ol>
  <li><p>When I run a docker container, where are those dependencies installed? If, for example, my host machine doesn't have <code>dependency A</code>, then when I run a docker container that require it, where does it install it to run the container?</p></li>
  <li><p>If it gets installed, is it isolated to that docker container only? If I wanted to use <code>dependency A</code> on my host machine, would I be able to from the installed version from the docker container or do I have to install it again on my host machine?</p></li>
  <li><p>Is the dependency installed multiple times per docker container? If I have 5 running containers of <code>image A</code> and 10 containers of <code>image B</code>, it doesn't install <code>dependency A v1.0</code> 5 times and <code>dependency A v2.0</code> 10 times, right?</p></li>
  </ol>