zero downtime deployment rolling update

README.md

1. Create the deployment and expose it using a Load Balancer

 kubectl apply -f demo.yaml

2. Wait for the LoadBalancer

$ kubectl get services lb-service --watch
NAME         TYPE           CLUSTER-IP    EXTERNAL-IP     PORT(S)        AGE
lb-service   LoadBalancer   10.76.7.155   35.205.231.57   80:30526/TCP   10m

3. Poll the application constantly

$ while true; do curl 35.205.231.57/hostname; echo ; sleep 1; done

server-deployment-8c8d64764-jsmsm
server-deployment-8c8d64764-jsmsm
server-deployment-8c8d64764-sggwl
server-deployment-8c8d64764-jsmsm
server-deployment-8c8d64764-sggwl

4. Update the deployment image and observe how the pods names change without any disruption

kubectl set image deployment/server-deployment agnhost=k8s.gcr.io/e2e-test-images/agnhost:2.40

demo.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: server-deployment
  labels:
    app: MyApp
spec:
  replicas: 2
  selector:
    matchLabels:
      app: MyApp
  template:
    metadata:
      labels:
        app: MyApp
    spec:
      terminationGracePeriodSeconds: 30
      containers:
      - name: agnhost
        image: k8s.gcr.io/e2e-test-images/agnhost:2.39
        args:
          - netexec
          - --http-port=80
          - --delay-shutdown=30
---
apiVersion: v1
kind: Service
metadata:
  name: lb-service
spec:
  type: LoadBalancer
  externalTrafficPolicy: Local
  selector:
    app: MyApp
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80