title: DRY docker-compose
body: <p>I'm trying to find a more DRY way to use docker-compose env.</p>
  
  <p>docker-compose-base.yml</p>
  
  <pre><code>base:
      image: reactjs_web
      volumes:
          - src:/reactjs/src
          - bin/server:/reactjs/bin/server
          - config:/reactjs/config
  </code></pre>
  
  <p>docker-compose-prod.yml</p>
  
  <pre><code>svr:
    extends:
      file: docker-compose-base.yml
      service: base
    command: npm run prod:deploy
    ports:
      - "8081:8081"
    environment:
      NODE_ENV: production
      PORT: "8081"
      CLTPORT: "8082"
  
  clt:
    extends:
      file: docker-compose-base.yml
      service: base
    command: npm run prod:deploy:clientside
    ports:
      - "8082:8082"
    environment:
      NODE_ENV: production
      PORT: "8082"
  </code></pre>
  
  <ul>
  <li>The ports and the env port are equals</li>
  <li>Is there a way to reference the clt port to the svr container ?</li>
  </ul>