Rolling update

Learn Deployment image updates.

Rolling update

When the pod template changes (e.g. the image), the Deployment does a rolling update: it opens a pod in the new ReplicaSet and, once it's ready, closes one of the old ones. Two settings determine speed and safety:

maxSurge: at most how many extra pods can be opened above the desired count.
maxUnavailable: at most how many pods can be out of service during the update.

spec:
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0

maxUnavailable: 0 guarantees capacity never drops.

Updating the image

The fastest way is kubectl set image; but for a lasting record, editing the YAML and running apply is better. An annotation can be added to write the reason for the change into the history:

kubectl set image deployment/web nginx=nginx:1.27.3
kubectl annotate deployment/web kubernetes.io/change-cause="nginx 1.27.3'e yükseltme"
kubectl rollout status deployment/web

Exercise A safe update

Write three commands: set the image of the nginx container in the web deployment to nginx:1.27.3; add the kubernetes.io/change-cause annotation as "nginx 1.27.3"; wait for the rollout to finish.

Show example solution

kubectl set image deployment/web nginx=nginx:1.27.3
kubectl annotate deployment/web kubernetes.io/change-cause="nginx 1.27.3"
kubectl rollout status deployment/web

Test yourself

If the readiness check (readinessProbe) always fails on new pods, what does the rolling update do?
- It stalls; the old pods keep serving
- It closes all the old pods
- It rolls back automatically
- It ignores readiness
Show answer

It stalls; the old pods keep serving — The old pod isn't closed until a new one is ready; after progressDeadlineSeconds the deployment is marked failed.

Change the container's image.

kubectl set image deployment/web ____=nginx:1.27.3

Show answer

kubectl set image deployment/web nginx=nginx:1.27.3

Match.

maxSurge

Extra pod limit
maxUnavailable

Unavailable pod limit
set image

Change image
change-cause

Reason for change

Next lesson: Rollback

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