7. Scaling, updates, and rollbacks
7.1. Scaling
To scale an existing deployment, use kubectl scale.
$ kubectl create -f nginx-deployment.yaml
deployment.apps/nginx-deployment created
$ kubectl get deploy
NAME READY UP-TO-DATE AVAILABLE AGE
nginx-deployment 3/3 3 3 11s
$ kubectl scale deploy nginx-deployment --replicas=1
deployment.apps/nginx-deployment scaled
$ kubectl get deploy
NAME READY UP-TO-DATE AVAILABLE AGE
nginx-deployment 1/1 1 1 58s
7.2. Rollout history
$ kubectl rollout status deploy nginx-deployment
deployment "nginx-deployment" successfully rolled out
$ kubectl rollout history deploy nginx-deployment
deployment.apps/nginx-deployment
REVISION CHANGE-CAUSE
1 <none>
$ kubectl rollout history deploy nginx-deployment --revision=1
deployment.apps/nginx-deployment with revision #1
Pod Template:
Labels: app=nginx-deployment
pod-template-hash=d64d454c6
Containers:
nginx:
Image: nginx:1.27.0-bookworm
Port: 80/TCP
Host Port: 0/TCP
Environment: <none>
Mounts: <none>
Volumes: <none>
Node-Selectors: <none>
Tolerations: <none>
7.3. Changing the deployed image
$ kubectl set image deploy nginx-deployment nginx=nginx:1.27.0-alpine \
&& kubectl annotate deploy/nginx-deployment kubernetes.io/change-cause="image changed to 1.27.0-alpine"
deployment.apps/nginx-deployment image updated
deployment.apps/nginx-deployment annotated
$ kubectl get svc,deploy,rs,pod
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 10h
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/nginx-deployment 1/1 1 1 19m
NAME DESIRED CURRENT READY AGE
replicaset.apps/nginx-deployment-55458c4fc 1 1 0 2s
replicaset.apps/nginx-deployment-d64d454c6 1 1 1 19m
NAME READY STATUS RESTARTS AGE
pod/nginx-deployment-55458c4fc-g5zxg 0/1 ContainerCreating 0 2s
pod/nginx-deployment-d64d454c6-nhgnv 1/1 Running 0 19m
After a few seconds:
$ kubectl get svc,deploy,rs,pod
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 10h
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/nginx-deployment 1/1 1 1 20m
NAME DESIRED CURRENT READY AGE
replicaset.apps/nginx-deployment-55458c4fc 1 1 1 55s
replicaset.apps/nginx-deployment-d64d454c6 0 0 0 20m
NAME READY STATUS RESTARTS AGE
pod/nginx-deployment-55458c4fc-g5zxg 1/1 Running 0 55s
$ kubectl rollout history deploy nginx-deployment
deployment.apps/nginx-deployment
REVISION CHANGE-CAUSE
1 <none>
2 image changed to 1.27.0-alpine
$ kubectl rollout history deploy nginx-deployment --revision=2
deployment.apps/nginx-deployment with revision #2
Pod Template:
Labels: app=nginx-deployment
pod-template-hash=55458c4fc
Annotations: kubernetes.io/change-cause: image changed to 1.27.0-alpine
Containers:
nginx:
Image: nginx:1.27.0-alpine
Port: 80/TCP
Host Port: 0/TCP
Environment: <none>
Mounts: <none>
Volumes: <none>
Node-Selectors: <none>
Tolerations: <none>
Note that the old replica set is still present, but with zero pods. The number of old replica sets retained is determined by the .spec.revisionHistoryLimit field of the deployment if present(default 10).
7.4. Reverting to a previous rollout
$ kubectl create -f nginx-deployment.yaml
deployment.apps/nginx-deployment created
$ kubectl set image deploy nginx-deployment nginx=nginx:1.24.0-alpine \
&& kubectl annotate deploy/nginx-deployment \
kubernetes.io/change-cause="image changed to 1.24.0-alpine"
deployment.apps/nginx-deployment image updated
deployment.apps/nginx-deployment annotated
$ kubectl set image deploy nginx-deployment nginx=nginx:1.25.0-alpine \
&& kubectl annotate deploy/nginx-deployment \
kubernetes.io/change-cause="image changed to 1.25.0-alpine"
deployment.apps/nginx-deployment image updated
deployment.apps/nginx-deployment annotated
$ kubectl set image deploy nginx-deployment nginx=nginx:1.26.0-alpine \
&& kubectl annotate deploy/nginx-deployment \
kubernetes.io/change-cause="image changed to 1.26.0-alpine"
deployment.apps/nginx-deployment image updated
deployment.apps/nginx-deployment annotated
$ kubectl set image deploy nginx-deployment nginx=nginx:1.27.0-alpine \
&& kubectl annotate deploy/nginx-deployment \
kubernetes.io/change-cause="image changed to 1.27.0-alpine"
deployment.apps/nginx-deployment image updated
deployment.apps/nginx-deployment annotated
$ kubectl rollout history deploy nginx-deployment
deployment.apps/nginx-deployment
REVISION CHANGE-CAUSE
1 <none>
2 image changed to 1.24.0-alpine
3 image changed to 1.25.0-alpine
4 image changed to 1.26.0-alpine
5 image changed to 1.27.0-alpine
Here we rollback to Revision #3:
$ kubectl rollout undo deploy/nginx-deployment --to-revision=3
deployment.apps/nginx-deployment rolled back
$ kubectl rollout history deploy nginx-deployment
deployment.apps/nginx-deployment
REVISION CHANGE-CAUSE
1 <none>
2 image changed to 1.24.0-alpine
4 image changed to 1.26.0-alpine
5 image changed to 1.27.0-alpine
6 image changed to 1.25.0-alpine
Note that Revision 3 has disappeared, which can be confusing; it may be preferable to simply reapply the changes associated with the original revision instead. This is because revisions are associated with replica sets, and we are re-using the replica set associated with the nginx:1.25.0-alpine image.