title: Transform docker-compose environment variable's value to service ip address
body: <p>I want to convert the environtment variable's value (it is a service in the same docker-compose.yml file) to the ip of that respective container and i can't achieve this.</p>
  
  <p>docker-compose.yml</p>
  
  <pre><code>version: '3'
  services:
    server:
      restart: always
      build:
        dockerfile: Dockerfile
        context: ./server
      ports:
        - '3001:3001'
      volumes: 
        - /app/node_modules
        - ./server:/app
    client:
      restart: always
      build:
        dockerfile: Dockerfile
        context: ./client
      ports:
        - '3000:3000'
      volumes: 
        - /app/node_modules
        - ./client:/app
      environment:
        - REACT_APP_API_HOST=server #I WANT TO TRANSFORM THIS TO THE SERVICE IP
        - REACT_APP_API_PORT=3001
  </code></pre>
  
  <p>When i console.log(process.env.REACT_APP_API_HOST) i get "server" in the console and i want this to be the ip address of the server (it's an api)</p>
  
  <p>Thanks.</p>