Probes

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Goal

Add a readinessProbe and a livenessProbe to the web container so Kubernetes knows when the pod is ready to accept traffic and when it needs to be restarted.

Why

Without probes:

• Readiness — Kubernetes sends traffic to pods immediately after they start, even if the app hasn't finished initialising. Requests during a rollout hit a pod that isn't ready yet.
• Liveness — If the app deadlocks (process is alive but unresponsive), Kubernetes leaves the pod running forever. A liveness probe detects this and restarts the container.

Step 1 — Add probes to deployment.yaml

Open deployment.yaml and add readinessProbe and livenessProbe to the container spec (after the env block added in the previous page):

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web
spec:
  replicas: 1
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
        - name: nginx
          image: nginx:1.27
          ports:
            - containerPort: 80
          env:
            - name: GREETING
              valueFrom:
                configMapKeyRef:
                  name: web-config
                  key: GREETING
          readinessProbe:
            httpGet:
              path: /
              port: 80
            initialDelaySeconds: 2
            periodSeconds: 5
          livenessProbe:
            httpGet:
              path: /
              port: 80
            initialDelaySeconds: 5
            periodSeconds: 10

Apply:

kubectl apply -f deployment.yaml

Step 2 — Verify

Watch the pods until the readiness probe passes:

kubectl get pods -l app=web

Expected output once ready:

NAME                   READY   STATUS    RESTARTS   AGE
web-<hash>-<hash>      1/1     Running   0          20s

READY 1/1 means the readiness probe has passed and the pod is in the Service endpoints. Before the probe passes, you'll see 0/1.

Describe a pod to see the probe configuration:

kubectl describe pod -l app=web | grep -A10 Liveness

Checkpoint

The web Deployment now has both probes. Kubernetes will:

• Hold traffic away from pods until readinessProbe passes.
• Restart pods automatically when livenessProbe fails.

Next: 04 Resource requests and limits