Demo App to play with Kubernetes health checks

⚠️ This project is not actively maintained. As an alternative, use: https://github.com/kubernetes-up-and-running/kuard

The ruby sinatra app exposes two health endpoints:

• /health/ready
• /health/live

By default these endpoints return 200 OK with a sample JSON body.

To simulate that the app in unhealthy, we can delete the files in /tmp:

• /tmp/ready affects API endpoint /health/ready
• /tmp/live affects API endpoint /health/live

Additional endpoints

• / returns a simple Hello world\n (for curl and webbrowsers)
• /env returns all environment variables as JSON

Usage

Start the image with plain docker

$ docker run -d --rm -p 9292:9292 docker.io/kicm/healthcheck-demo

Open your browser and play with the different endpoints:

• http://localhost:9292/
• http://localhost:9292/env
• http://localhost:9292/health/live
• http://localhost:9292/health/ready

Example deployment in Kubernetes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: healthcheck-demo
spec:
  replicas: 3
  selector:
    matchLabels:
      app: healthcheck-demo
  template:
    metadata:
      labels:
        app: healthcheck-demo
    spec:
      containers:
      - name: app
        image: docker.io/kicm/healthcheck-demo
        ports:
        - containerPort: 9292
          name: http
        env:
          - name: FOO
            value: bar
          - name: HELLO
            value: world
        livenessProbe:
          httpGet:
            port: http
            path: /health/live
          periodSeconds: 5
        readinessProbe:
          httpGet:
            port: http
            path: /health/ready
          periodSeconds: 1

Now you can play with these endpoints. Let's make one Pod "not ready":

$ kubectl exec -ti healthcheck-demo-745554966d-f9jvz bash
www-data@healthcheck-demo-745554966d-f9jvz:/$ rm /tmp/ready

After 3 seconds you see that this Pod is not ready anymore (0/1 in column READY):

$ kubectl get pods
NAME                                READY   STATUS    RESTARTS   AGE
healthcheck-demo-745554966d-f9jvz   0/1     Running   0          4m45s
healthcheck-demo-745554966d-ghxqk   1/1     Running   0          4m39s
healthcheck-demo-745554966d-xwhp5   1/1     Running   0          4m42s

Let's make it unhealthy now: delete the file /tmp/live inside the Pod:

$ kubectl exec -ti healthcheck-demo-745554966d-f9jvz bash
www-data@healthcheck-demo-745554966d-f9jvz:/$ rm /tmp/live

After around 15 seconds, Kubernetes will restart this Pod and everything is fine again:

$ kubectl get pods
NAME                                READY   STATUS    RESTARTS   AGE
healthcheck-demo-745554966d-f9jvz   1/1     Running   1          6m52s
healthcheck-demo-745554966d-ghxqk   1/1     Running   0          6m46s
healthcheck-demo-745554966d-xwhp5   1/1     Running   0          6m49s