title: Re-using environment variables in docker-compose.yml
body: <p>Is it possible to re-use environment variables that are shared among multiple containers?</p>
  <p>The idea is to avoid duplication, as illustrated in this example:</p>
  <pre class="lang-yaml prettyprint-override"><code>version: '2'
  
  services:
  
    db:
      image: example/db
      ports:
        - &quot;8443:8443&quot; 
      container_name: db
      hostname: db
      environment:
        - USER_NAME = admin 
        - USER_PASSWORD = admin 
  
  svc:
    image: example/svc
    depends_on:
      - db
    ports:
      - &quot;9443:9443&quot;
    container_name: svc
    hostname: svc
    environment:
      - DB_URL = https://db:8443
      - DB_USER_NAME = admin
      - DB_USER_PASSWORD = admin 
  </code></pre>