Understanding Kubernetes Deployment Controller and Rolling Updates

The Deployment controller in Kubernetes manages stateless application services, handling pod and ReplicaSet lifecycle, providing features such as deployment, replica control, rolling updates, and rollbacks.

Rolling upgrades update instances in batches rather than all at once, reducing downtime. The controller reduces the old ReplicaSet replicas to zero while scaling the new ReplicaSet to the desired count. Two update strategies exist: Recreate (delete all old pods then create new ones) and RollingUpdate , which updates pods incrementally using maxUnavailable and maxSurge parameters.

Example Deployment manifest:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: haha-deploy
  namespace: dev
spec:
  replicas: 5
  revisionHistoryLimit: 5  # keep 5 historical versions
  strategy:
    type: RollingUpdate
  selector:
    matchLabels:
      app: haha-nginx-pod
  template:
    metadata:
      labels:
        app: haha-nginx-pod
    spec:
      containers:
      - name: haha-nginx
        image: nginx:1.23.0

To view controller parameters:

[root@master ~]# kubectl describe deploy haha-deploy -n dev

Rolling update the nginx image and record the change:

[root@master ~]# kubectl set image deployment/haha-deploy haha-nginx=nginx:1.23.0 -n dev --record=true

Monitor the upgrade process in real time:

[root@master ~]# kubectl get pods -n dev -w

Rollout commands for history, undo, pause, resume, and status:

[root@master ~]# kubectl rollout history deployment/haha-deploy -n dev

[root@master ~]# kubectl rollout undo deployment/haha-deploy -n dev --to-revision=2

[root@master ~]# kubectl rollout pause deployment/haha-deploy -n dev

[root@master ~]# kubectl rollout resume deployment/haha-deploy -n dev

[root@master ~]# kubectl rollout status deployment/haha-deploy -n dev

These commands allow operators to manage deployment versions, view change history, and safely roll back to previous releases, supporting continuous delivery in cloud‑native environments.