title: docker-compose scaling with unique environment variable
body: <p>I have a sample compute service in my docker-compose file which works just great as expected. </p>
  
  <pre><code>version: "3"
  services:
    compute-service:
      image: dummy/compute
      environment:
        - INPUT=2
  </code></pre>
  
  <p>However there could be times in which I need to run this service with diff inputs (say INPUT = 4, 7, 9, 10, 12..etc). I do not like the idea of copying and pasting the service multiple times for each input. Scaling is an option. But how can I ensure that each instance works on unique input variable. </p>
  
  <hr>
  
  <p>I am aware that I could use an env variable like this. My question is rather related to how to pass unique values as part of scaling!! </p>
  
  <pre><code>version: "3"
  services:
    compute-service:
      image: dummy/compute
      environment:
        - INPUT=${INPUT}
  </code></pre>