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Lab 3.4 - Configuring Health Checks

Objectives​

By the end of this lab, you will be able to:

  • Configure Liveness Probes
  • Configure Readiness Probes
  • Use Startup Probes
  • Observe probe behavior

Exercise 1: Liveness Probe​

Step 1: Create a Pod with a Liveness Probe​

Create pod-liveness.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: liveness-pod
spec:
  containers:
  - name: nginx
    image: nginx:1.20
    livenessProbe:
      httpGet:
        path: /
        port: 80
      initialDelaySeconds: 10
      periodSeconds: 5
      failureThreshold: 3

Step 2: Apply and observe​

kubectl apply -f pod-liveness.yaml

# Observe the events
kubectl describe pod liveness-pod

Exercise 2: Readiness Probe​

Step 1: Create a Pod with a Readiness Probe​

Create pod-readiness.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: readiness-pod
  labels:
    app: web
spec:
  containers:
  - name: nginx
    image: nginx:1.20
    readinessProbe:
      httpGet:
        path: /
        port: 80
      initialDelaySeconds: 5
      periodSeconds: 5

Step 2: Create a Service​

Create service.yaml:

apiVersion: v1
kind: Service
metadata:
  name: web-service
spec:
  selector:
    app: web
  ports:
  - port: 80

Step 3: Observe​

# View the Endpoints
kubectl get endpoints web-service

# The Pod appears in the Endpoints only when the readiness probe succeeds

Exercise 3: Startup Probe​

Step 1: Create a Pod with a Startup Probe​

Create pod-startup.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: startup-pod
spec:
  containers:
  - name: slow-app
    image: busybox
    command: ['sh', '-c', 'sleep 30 && echo "Ready" && sleep 3600']
    startupProbe:
      exec:
        command: ['sh', '-c', 'echo "started"']
      failureThreshold: 30
      periodSeconds: 2
    livenessProbe:
      exec:
        command: ['sh', '-c', 'echo "alive"']
      periodSeconds: 10

Step 2: Observe​

kubectl apply -f pod-startup.yaml

# Observe the startup
kubectl get pod startup-pod -w

# The liveness/readiness probes wait for the startup to succeed

Exercise 4: Failing Probe​

Step 1: Create a Pod with a failing probe​

Create pod-failing.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: failing-pod
spec:
  containers:
  - name: nginx
    image: nginx:1.20
    livenessProbe:
      httpGet:
        path: /nonexistent
        port: 80
      initialDelaySeconds: 5
      periodSeconds: 5
      failureThreshold: 3

Step 2: Observe the restart​

kubectl apply -f pod-failing.yaml

# Observe the restarts
kubectl get pod failing-pod -w

# View the events
kubectl describe pod failing-pod

Cleanup​

kubectl delete pod liveness-pod readiness-pod startup-pod failing-pod
kubectl delete service web-service

Reflection Questions​

  1. What is the difference between liveness and readiness?
  2. When to use a startup probe?
  3. What happens if a liveness probe fails?
  4. Why are readiness probes important for Services?

Next Steps​

Quiz Module 3: Validate your knowledge
Module 4: Services and Networking

Lab created: December 2024