title: Using --add-host or extra_hosts with docker-compose
body: <p>I am using <code>docker-compose</code> to run a test environment, that consists of about 5 different containers. The inter-container links and the shared volumes (volumes-from) works wonderfully. I also expose some ports up to the host machine, which works nicely.</p>
  
  <p>What I am missing is a way to link some of my real servers into this environment, without hardcoding ip address. With <code>docker run</code>, you could use <code>--add-host</code> to add another line in your <code>/etc/hosts</code> file. Is there any way to do something similar with docker-compose?</p>