Kubernetes Probes: Liveness, Readiness, and Startup

Health probes ensure your applications are running correctly and receiving traffic appropriately.

Probe Types

Probe	Purpose	Failure Action
Liveness	Is container healthy?	Restart container
Readiness	Is container ready for traffic?	Remove from Service
Startup	Has container started?	Kill container

Probe Mechanisms

HTTP Probe

livenessProbe:
  httpGet:
    path: /health
    port: 8080
    httpHeaders:
    - name: Custom-Header
      value: Awesome
  initialDelaySeconds: 5
  periodSeconds: 10
  failureThreshold: 3

TCP Probe

livenessProbe:
  tcpSocket:
    port: 3306
  initialDelaySeconds: 15
  periodSeconds: 20

Exec Probe

livenessProbe:
  exec:
    command:
    - cat
    - /tmp/healthy
  initialDelaySeconds: 5
  periodSeconds: 5

Probe Configuration

Parameter	Description	Default
`initialDelaySeconds`	Delay before first probe	0
`periodSeconds`	How often to probe	10
`timeoutSeconds`	Probe timeout	1
`successThreshold`	Min consecutive successes	1
`failureThreshold`	Failures before action	3

Liveness Probe

Restarts container if unhealthy:

apiVersion: v1
kind: Pod
metadata:
  name: liveness-demo
spec:
  containers:
  - name: app
    image: my-app
    livenessProbe:
      httpGet:
        path: /healthz
        port: 8080
      initialDelaySeconds: 10
      periodSeconds: 5
      failureThreshold: 3

Readiness Probe

Removes pod from service if not ready:

spec:
  containers:
  - name: app
    image: my-app
    readinessProbe:
      httpGet:
        path: /ready
        port: 8080
      initialDelaySeconds: 5
      periodSeconds: 5

Startup Probe

For slow-starting applications. Disables other probes until success:

spec:
  containers:
  - name: app
    image: slow-starter
    startupProbe:
      httpGet:
        path: /started
        port: 8080
      failureThreshold: 30
      periodSeconds: 10
    livenessProbe:
      httpGet:
        path: /healthz
        port: 8080

Complete Example

apiVersion: v1
kind: Pod
metadata:
  name: probe-demo
spec:
  containers:
  - name: app
    image: my-app
    ports:
    - containerPort: 8080
    startupProbe:
      httpGet:
        path: /started
        port: 8080
      failureThreshold: 30
      periodSeconds: 10
    livenessProbe:
      httpGet:
        path: /healthz
        port: 8080
      periodSeconds: 10
    readinessProbe:
      httpGet:
        path: /ready
        port: 8080
      periodSeconds: 5

Best Practices

Always configure readiness probes
Use startup probe for slow apps
Keep probe endpoints lightweight
Don’t check dependencies in liveness
Set appropriate thresholds

Practice Health Probes

Probe configuration appears in CKAD exams. Practice at Sailor.sh.

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