What is a Kubernetes Deployment?

Short answer

A Kubernetes Deployment is a controller that manages a set of identical Pods. It ensures the desired number of replicas are running, supports rolling updates, and enables rollback to previous versions.

How it works

The Deployment controller maintains a ReplicaSet to manage Pods. When you update the Deployment, it creates a new ReplicaSet with the updated Pod template and gradually scales it up while scaling the old one down. If something goes wrong, you can roll back to a previous revision.

Example

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
      - name: nginx
        image: nginx:1.25
        ports:
        - containerPort: 80

Why it matters

Deployments provide declarative updates for stateless applications. They automate scaling, self-healing, and zero-downtime updates, forming the backbone of most Kubernetes workloads.

Common issues

• Updating only the container tag may not trigger a rollout if the image pull policy is IfNotPresent.
• Resource limits should be set to prevent runaway Pods.
• Rollbacks do not restore deleted ConfigMaps or Secrets.