title: How to set dynamic values with Kubernetes yaml file
body: <p>For example, a deployment yaml file:</p>
  
  <pre><code>apiVersion: extensions/v1beta1
  kind: Deployment
  metadata:
    name: guestbook
  spec:
    replicas: 2
    template:
      metadata:
        labels:
          app: guestbook
        spec:
          container:
            - name: guestbook
              image: {{Here want to read value from config file outside}}
  </code></pre>
  
  <p>There is a <code>ConfigMap</code> feature with Kubernetes, but that's also write the key/value to the yaml file. Is there a way to set the key to environment variables?</p>