title: Why does `docker-compose up` erase volumes?
body: <p>I'm testing lots of services as containers, usually through docker-compose.</p>
  
  <p>Since I'm new to docker this question can appear noobish, anyway.</p>
  
  <p>At some point I had a docker-compose stack (few containers with volumes) running. I had to stop containers to re-use the same ports; I did that with <code>docker stop</code> command.</p>
  
  <p>When I was ready to start my containers again I did:</p>
  
  <pre><code>$ docker-compose start
  Starting jenkins   ... done
  Starting gitlab-ce ... done
  ERROR: No containers to start
  </code></pre>
  
  <p>I checked for containers and was surprised to see this:</p>
  
  <pre><code>$ docker-compose ps
  Name   Command   State   Ports
  ------------------------------
  </code></pre>
  
  <p>So I ran:</p>
  
  <pre><code>$ docker-compose up
  Creating volume "dockerpipelinejenkins_jenkins_home" with default driver
  Creating volume "dockerpipelinejenkins_gitlab_logs" with default driver
  Creating volume "dockerpipelinejenkins_gitlab_data" with default driver
  Creating volume "dockerpipelinejenkins_gitlab_config" with default driver
  Creating dockerpipelinejenkins_jenkins_1   ... done
  Creating dockerpipelinejenkins_gitlab-ce_1 ... done
  Attaching to dockerpipelinejenkins_jenkins_1, dockerpipelinejenkins_gitlab-ce_1
  </code></pre>
  
  <p>... and I was shocked to see that my volumes had been recreated, effectively erasing my data.</p>
  
  <p>Why did docker compose erase the volumes, and will it happen every time when I stop docker containers using <code>docker stop</code>?</p>