Application life cycle management.md

Application life cycle management

Install process

Install nginx 1.12.2 with 2 pods

Create deployment template with nginx version 1.12.2

kubectl create  deployment nginx --save-config=true --image=nginx:1.12.2 --dry-run=client -o yaml > nginx.yaml

Edit nginx.yaml to update replicas count.

edit nginx.yaml

Apply deployment template to Kubernetes cluster

kubectl apply --record=true -f nginx.yaml

Scale

Scale up to 4 pods

kubectl scale deployment nginx --replicas 4

Scale down to 2 pods

kubectl scale deployment nginx --replicas 2

Upgrade

Upgrade nginx to 1.13.8

Update deployment container image with kubectl set image

kubectl set image --record=true deployment/nginx nginx=nginx:1.13.8
deployment.apps/nginx image updated

Use --record=true to save what caused the deployment

kubectl get pods
NAME                     READY   STATUS              RESTARTS   AGE
nginx-76d56bc6fb-cdrdl   0/1     ContainerCreating   0          3s
nginx-8f4745b9c-4lbwn    1/1     Running             0          5m51s
nginx-8f4745b9c-8rflb    1/1     Running             0          5m51s

Another option to upgrade is to patch deployment

Patch nginx deployment with latest version

kubectl patch deployment nginx --type json -p='[{"op":"replace","path":"/spec/template/spec/containers/0/image","value":"nginx:latest"}]'
deployment.apps/nginx patched

Lets check patching result

kubectl get deployments.apps nginx -o json | jq ".spec.template.spec.containers[0].image"
"nginx:latest"

Lets check deployment history

kubectl rollout history deployment nginx
deployment.apps/nginx
REVISION  CHANGE-CAUSE
1         <none>
3         kubectl set image deployment/nginx nginx=nginx:1.14.8 --record=true
4         kubectl set image deployment/nginx nginx=nginx:1.13.8 --record=true
5         kubectl set image deployment/nginx nginx=nginx:1.13.8 --record=true
6         kubectl set image deployment/nginx nginx=nginx:1.13.8 --record=true

Rollback

Lets make faulty deployment

Upgrade nginx to 1.14.8 which doesn't exist

kubectl set image deployment/nginx nginx=nginx:1.14.8 --record

Check upgrade status

kubectl rollout status deployment nginx
Waiting for deployment "nginx" rollout to finish: 1 out of 2 new replicas have been updated...

kubectl is waiting for deployment to finish which will not happen due to incorrect image name. So, we need to rollback the deployment. Press Ctrl+C to stop waiting for kubectl rollout status update.

Rollback latest deployment

Undo the current deployment

kubectl rollout undo deployment nginx
deployment.apps/nginx rolled back

Check deployment history

kubectl rollout history deployment nginx
deployment.apps/nginx
REVISION  CHANGE-CAUSE
1         <none>
4         kubectl set image deployment/nginx nginx=nginx:1.13.8 --record=true
5         kubectl set image deployment/nginx nginx=nginx:1.13.8 --record=true
7         kubectl set image deployment/nginx nginx=nginx:1.14.8 --record=true
8         kubectl set image deployment/nginx nginx=nginx:1.13.8 --record=true

Notice that undo command moved revision record 6 to record 8 in history of deployment. So, it tell operators that rollback was applied.