title: How can I use environment variable in kubernetes replication controller yaml file
body: <p>How to read environment variables in kubernetes yaml file?
  for example, I want to change the docker image tag but do not want to rewrite the file, like this</p>
  
  <pre><code>apiVersion: v1
  kind: ReplicationController
  ...
  spec:
    containers:
      - name: myapp
        image: myapp:${VERSION}
   ...
  </code></pre>
  
  <p>With this I can do <code>kubectl rolling-update</code> without updating the yaml file.</p>
  
  <p>thanks</p>