Rolling updates in kubernetes

Rolling updates in kubernetes deployment

Managed using deployments.

Rolling update: allows deployment to use new updates without downtime via gradual replacement of old pods with new updated ones.

Change can be anything in the pod template that is part of the deployment manifest.

Rollback: If there is a problem in the rolling update, we can go back to previous deployment revision.

Example :

nginx-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

rollouts can be done via kubectl edit deployment DEPLOYMENT_NAME

or using kubectl apply -f DEPLOYMENT_MANIFEST.yaml after edits.

you can check the status of the deployment rollout using

kubectl rollout status deployment.v1.apps/DEPLOYMENT_NAME

before applying things we need to make sure that we use --record flag for keeping track of the change cause.

Example for nginx-deployment.yaml and nginx-deployment :

kubectl apply --filename=nginx-deployment.yaml --record=true

kubectl edit deployment nginx-deployment --record=true

Check the rollout status using: kubectl rollout history deployment.v1.apps/nginx-deployment or kubectl rollout history deployment nginx-deployment

Example of rollout and rollback

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.16
---
apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  clusterIP: 10.96.0.239
  selector:
    app: nginx
  ports:
  - name: name-of-service-port
    protocol: TCP
    port: 80
    targetPort: 80

so we will do 3 rollouts in order from nginx:1.16 to nginx:1.17 to nginx:1.18

rollback deployment

Deployment can be rolled back using kubectl rollout undo to a specific revision or to the previous revision.

kubectl rollout undo deployment nginx-deployment --to-revision=1