• When first creating a Deployment, it triggers a Rollout.
  • A new Rollout creates a new Deployment Revision
  • When the application is updated in the future i.e. to a newer version (Revision 2) nginx 1.7.0 –> nginx 1.7.1
  • Can see the rollout status with this command: 
    kubectl rollout status deployment/myapp-deployment
  • To see the history and revisions of the deployment, run this command: 
    kubectl rollout history deployment/myapp-deployment
  • Deployment Strategy
    • One way is to destroy all pods of X version and upgrade them with Y version.
    • The problem is there is a period where all applications are down, but the upgraded applications come back up. This is known as Recreat.
    • The second and better strategy is to take down each deployment and bring it back up with the new version one by one. This is known as Rolling Update
  • Regarding kubectl apply to update the image from image: nginx to image: nginx:1.7.1: ``` apiVersion: kind: metadata: spec: deployment-definition.yml name: myapp-deployment labels: app: myapp type: front-end apps/v1 metadata: name: myapp-pod labels: app: myapp type: front-end spec: containers:
  • name: nginx-container image: nginx:1.7.1 replicas: selector: matchLabels: type: front-end ```
  • Just run kubectl apply -f deployment-definition.yml and this will create a new rollout with the changes. A new revision of the deployment is created.
  • To update the image of your application, use the kubectl set image deployment/myapp-deployment nginx container=nginx:1.9.1
    • Doing it this way means the deployment definition file will have a different configuration.
  • Run kubectl describe deployment to see deployment details.
    • Can see the Recreate and Rolling in action.
  • When first deployed, the Replica Set will be deployed.
    • When the Rollout begins, under the hood a Replica Set-2 is created. Then in Replica Set - 1, the pods are slowly removed and then upgraded versions are added to Replica Set - 2.
    • This can be seen in action by running the kubectl get replicasets command.
  • How do you Rollback and update?
    • To rollback to a previous version of the app in all instances, can run kubectl rollout undo deployment/myapp-deploym
    • Then pods will be destroyed in the new Replica Set and the older pods will be brought back up in the previuous Replica Set.
  • Can compare Rollback with kubectl get replicasets.
  • To see the history of the Rollout commands, run: 
    kubectl rollout status deployment/myapp-deployment
kubectl rollout history deployment/myapp-deployment

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