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Step 7: Live and Ready

Remember that both our rolling update (seen in Step 2) and our setting/unsetting env variables (seen in Step 5) caused the pods to "restart". The problem is that clients (polling curl) also received error messages during this "downtime".

$ kubectl scale --replicas=3 deployment/myboot
$ IP=$(minikube --profile 9steps ip)
$ PORT=$(kubectl get service myboot -o jsonpath="{.spec.ports[*].nodePort}")
$ while true; do curl $IP:$PORT; sleep .3; done
$ kubectl set image deployment/myboot myboot=9stepsawesome/myboot:v2
$ kubectl set image deployment/myboot myboot=9stepsawesome/myboot:v1

Now, let’s have a zero-downtime rolling update/deployment.

Add the Liveness and Readiness probe to your deployment yaml.

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  labels:
    app: myboot
  name: myboot
spec:
  replicas: 1
  selector:
    matchLabels:
      app: myboot
  template:
    metadata:
      labels:
        app: myboot
    spec:
      containers:
      - name: myboot
        image: 9stepsawesome/myboot:v1
        ports:
          - containerPort: 8080
        envFrom:
        - configMapRef:
            name: my-config
        resources:
          requests:
            memory: "300Mi"
            cpu: "250m" # 1/4 core
          limits:
            memory: "400Mi"
            cpu: "1000m" # 1 core
        livenessProbe:
          httpGet:
              port: 8080
              path: /
          initialDelaySeconds: 10
          periodSeconds: 5
          timeoutSeconds: 2
        readinessProbe:
          httpGet:
            path: /health
            port: 8080
          initialDelaySeconds: 10
          periodSeconds: 3

and replace the current Deployment in the current environment

$ kubectl replace -f kubefiles/myboot-deployment-liveready.yml

and do a describe to see the new probes in place.

$ kubectl describe deployment/myboot
...
   myboot:
    Image:      9stepsawesome/myboot:v1
    Port:       8080/TCP
    Host Port:  0/TCP
    Limits:
      cpu:     1
      memory:  400Mi
    Requests:
      cpu:      250m
      memory:   300Mi
    Liveness:   http-get http://:http/ delay=10s timeout=2s period=5s #success=1 #failure=3
    Readiness:  http-get http://:8080/health delay=10s timeout=1s period=3s #success=1 #failure=3
    Environment Variables from:
      my-config   ConfigMap  Optional: false
...

now try the rolling update with the poller hitting the endpoints

start the poller in terminal 1

#!/bin/bash

while true
do
  curl $(minikube --profile 9steps ip):$(kubectl get service/myboot -o jsonpath="{.spec.ports[*].nodePort}")
  sleep .3;
done

scale up to 2 replicas

$ kubectl scale deployment/myboot --replicas=2

Make sure you have v2 of the Spring Boot image ready. Change the Java code to say 'Bonjour' and rebuild

$ mvn clean package
$ docker build -t 9stepsawesome/myboot:v2 .

now rollout the update

$ kubectl set image deployment/myboot myboot=9stepsawesome/myboot:v2

and there will no errors

Aloha from Spring Boot! 115 on myboot-859cbbfb98-lnc8q
Aloha from Spring Boot! 116 on myboot-859cbbfb98-lnc8q
Aloha from Spring Boot! 117 on myboot-859cbbfb98-lnc8q
Bonjour from Spring Boot! 0 on myboot-5b686c586f-ccv5r
Bonjour from Spring Boot! 1 on myboot-5b686c586f-ccv5r

Rolling back is also as clean

$ kubectl rollout undo deployment/myboot
Bonjour from Spring Boot! 30 on myboot-5b686c586f-ccv5r
Bonjour from Spring Boot! 31 on myboot-5b686c586f-ccv5r
Bonjour from Spring Boot! 32 on myboot-5b686c586f-ccv5r
Aloha from Spring Boot! 0 on myboot-859cbbfb98-4rvl8
Aloha from Spring Boot! 1 on myboot-859cbbfb98-4rvl8

Once you understand the basics then you can try the advanced demonstration. Where a stateful shopping cart is preserved across a rolling update based on leveraging the readiness probe.