Rolling update

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Goal

Change the web Deployment's image tag from nginx:1.27 to nginx:1.27.1 and watch Kubernetes replace pods gradually so the app stays available throughout.

Why

Without a rolling update strategy, changing the image would require taking the old pods down and bringing new ones up — causing downtime. Kubernetes RollingUpdate (the default) brings new pods up before removing old ones, so there is always at least one healthy pod serving traffic.

Step 1 — Update the image tag in deployment.yaml

Open deployment.yaml and change the image line:

          image: nginx:1.27.1

The full container spec with all additions so far:

      containers:
        - name: nginx
          image: nginx:1.27.1
          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
          resources:
            requests:
              cpu: "50m"
              memory: "64Mi"
            limits:
              cpu: "200m"
              memory: "128Mi"

Apply:

kubectl apply -f deployment.yaml

Step 2 — Watch the rollout

kubectl rollout status deployment/web

Kubernetes prints a progress line for each pod it replaces and exits with code 0 when the rollout completes:

Waiting for deployment "web" rollout to finish: 0 of 1 updated replicas are available...
deployment "web" successfully rolled out

Step 3 — Check rollout history

kubectl rollout history deployment/web

Expected output:

deployment.apps/web
REVISION  CHANGE-CAUSE
1         <none>
2         <none>

Revision 1 is the original nginx:1.27 image; revision 2 is nginx:1.27.1.

Step 4 — Roll back if needed

If something goes wrong, undo the last rollout:

kubectl rollout undo deployment/web

Kubernetes restores revision 1 using the same rolling strategy.

Checkpoint

You updated the image tag and Kubernetes replaced the pod without downtime. The rollout history gives you a safety net to undo.

Next: 06 Scaling