title: Link containers env
body: <p>Im trying to link two containers to one app, and want to reference those apps hostname/url in an env.</p>
  
  <p>Then the main application can run, but i cannot manage to get the values properly.</p>
  
  <p>Dockerfile of main app contains this</p>
  
  <pre><code>ENV APP1_URL app1
  
  ENV APP2_URL app2
  </code></pre>
  
  <p>When running </p>
  
  <pre><code>docker run -d -p 22222:3000 --link app1:app1 app2:app2 --name mainapp user/image
  </code></pre>
  
  <p>Main app needs those env to run, how can i get those values? </p>