title: How to keep Docker container volume files?
body: <p>I'd like to share <code>~/mydir</code> directory with host, but not replace Docker container directory with host files.
  So, I have <code>docker-compose.yml</code></p>
  
  <pre><code>version: '2'
  services:
    app:
      container_name: mono
      build: .
      volumes:
        # save .composer files on host to keep cache warmed up
        - '/srv/mono/mydir:/root/mydir'
      command: sleep infinity
  </code></pre>
  
  <p>And <code>Dockerfile</code></p>
  
  <pre><code>#/bin/bash
  FROM php:5.6
  
  RUN mkdir /root/mydir &amp;&amp; echo '{}' &gt; /root/mydir/myfile.json
  
  VOLUME /root/mydir
  </code></pre>
  
  <p>Directory <code>/srv/mono/mydir</code> is empty. It was replaced with host directory. It's clear.</p>
  
  <p>But how to keep original files?</p>
  
  <p>For example it work for MySQL Percona containers:</p>
  
  <pre><code>version: '2'
  services:
    percona-56:
      container_name: percona-56
      image: percona/percona-server:5.6
      volumes:
      - /srv/mysql/percona-56:/var/lib/mysql
      environment:
        MYSQL_ALLOW_EMPTY_PASSWORD: 'yes'
  </code></pre>
  
  <p>There are original files from the container:</p>
  
  <pre><code>$ ll /srv/mysql/percona-56
  total 176220
      auto.cnf
      error.log
      ibdata1
      ib_logfile0
      ib_logfile1
      init.ok
      mysql
      performance_schema
  </code></pre>
  
  <p>I've tried to inspect <a href="https://github.com/docker-library/percona/blob/0366da072fe5dc95af26d8a9f9ace48c72670720/5.6/Dockerfile" rel="noreferrer">Percona Dockerfile</a> but didn't find something related to the volume sharing.</p>
  
  <pre><code>$ docker --version
  Docker version 1.12.3, build 6b644ec
  </code></pre>