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Chapter 3.8 - Health Checks

Learning Objectives​

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

  • Understand the three types of probes
  • Configure Liveness Probes
  • Configure Readiness Probes
  • Use Startup Probes
  • Choose the right health check strategy

Types of Probes​

Kubernetes provides three types of probes to check the health of containers:

1. Liveness Probe​

Determines if the container should be restarted.

Example​

livenessProbe:
  httpGet:
    path: /health
    port: 8080
  initialDelaySeconds: 30
  periodSeconds: 10
  timeoutSeconds: 5
  failureThreshold: 3

Behavior​

If the probe fails: The container is restarted.

2. Readiness Probe​

Determines if the container is ready to receive traffic.

Example​

readinessProbe:
  httpGet:
    path: /ready
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 5
  timeoutSeconds: 3
  successThreshold: 1
  failureThreshold: 3

Behavior​

If the probe fails: The Pod is removed from the Service Endpoints.

3. Startup Probe​

For applications that are slow to start.

Example​

startupProbe:
  httpGet:
    path: /startup
    port: 8080
  failureThreshold: 30    # 30 attempts
  periodSeconds: 10       # Every 10 seconds
  # Total: up to 5 minutes

Behavior​

During startup: Other probes are disabled.

Probe Types​

HTTP GET​

livenessProbe:
  httpGet:
    path: /health
    port: 8080
    httpHeaders:
    - name: Custom-Header
      value: Awesome

TCP Socket​

livenessProbe:
  tcpSocket:
    port: 8080

Command Exec​

livenessProbe:
  exec:
    command:
    - cat
    - /tmp/healthy

Complete Configuration​

apiVersion: v1
kind: Pod
metadata:
  name: healthy-pod
spec:
  containers:
  - name: app
    image: my-app:1.0
    ports:
    - containerPort: 8080
    livenessProbe:
      httpGet:
        path: /health
        port: 8080
      initialDelaySeconds: 30
      periodSeconds: 10
      failureThreshold: 3
    readinessProbe:
      httpGet:
        path: /ready
        port: 8080
      initialDelaySeconds: 5
      periodSeconds: 5
      failureThreshold: 3
    startupProbe:
      httpGet:
        path: /startup
        port: 8080
      failureThreshold: 30
      periodSeconds: 10

Best Practices​

When to Use Each Probe​

  • Liveness: If the application can become stuck
  • Readiness: If the application needs time to be ready
  • Startup: If the application starts slowly (>30s)
  • initialDelaySeconds: Long enough for startup
  • periodSeconds: 5-10 seconds
  • timeoutSeconds: 1-3 seconds
  • failureThreshold: 3 (default)

Summary​

In this chapter, you learned:

Liveness Probe: Restarts the container if it crashes
Readiness Probe: Removes the Pod from the Service if it is not ready
Startup Probe: For applications that are slow to start
Types: HTTP GET, TCP Socket, Command Exec
Configuration: initialDelaySeconds, periodSeconds, failureThreshold

Next Steps​

Now that you have mastered Health Checks:

Lab 3.4: Configuring Health Checks
Quiz Module 3: Validate your knowledge

Chapter created: December 2024