Scaling and Rolling Updates

The API server allows for the configurations settings to be updated for most values. There are some immutable values, which may be different depending on the version of Kubernetes you have deployed.

A common update is to change the number of replicas running. If this number is set to zero, there would be no containers, but there would still be a ReplicaSet and Deployment. This is the backend process when a Deployment is deleted.

$ kubectl scale deploy/dev-web --replicas=4

deployment "dev-web" scaled

$ kubectl get deployments

NAME READY UP-TO-DATE AVAILABLE AGE

dev-web 4/4 4 4 20s

Non-immutable values can be edited via a text editor, as well. Use edit to trigger an update. For example, to change the deployed version of the nginx web server to an older version:

$ kubectl edit deployment nginx

....
      containers:
      - image: nginx:1.8 #<<---Set to an older version 
        imagePullPolicy: IfNotPresent
                name: dev-web
....

This would trigger a rolling update of the deployment. While the deployment would show an older age, a review of the Pods would show a recent update and older version of the web server application deployed.