Kubernetes Deployments

A Deployment manages a set of identical pod replicas. It ensures the desired number of pods are running, handles rolling updates, and enables rollback.

Deployment YAML

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
        - name: my-app
          image: myrepo/my-app:1.0
          ports:
            - containerPort: 8080
          resources:
            requests:
              cpu: "100m"
              memory: "128Mi"
            limits:
              cpu: "500m"
              memory: "256Mi"

kubectl apply -f deployment.yaml
kubectl get deployments
kubectl get pods

Rolling Update Strategy

The default strategy replaces pods gradually with zero downtime:

strategy:
  type: RollingUpdate
  rollingUpdate:
    maxUnavailable: 1   # max pods that can be down during update
    maxSurge: 1         # max extra pods above desired count

Recreate is the alternative — it kills all old pods before starting new ones (causes downtime, useful when you cannot run two versions simultaneously).

Deploying a New Version

Update the image tag in the manifest and apply, or use kubectl set image:

kubectl set image deployment/my-app my-app=myrepo/my-app:2.0

# Watch the rollout progress
kubectl rollout status deployment/my-app

Rollback

# Undo to the previous version
kubectl rollout undo deployment/my-app

# Undo to a specific revision
kubectl rollout history deployment/my-app
kubectl rollout undo deployment/my-app --to-revision=2

Scaling

# Scale to 5 replicas
kubectl scale deployment my-app --replicas=5

# Or update replicas in the manifest and re-apply

Horizontal Pod Autoscaler

Automatically scale based on CPU/memory:

kubectl autoscale deployment my-app --min=2 --max=10 --cpu-percent=70

Or in YAML:

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: my-app-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: my-app
  minReplicas: 2
  maxReplicas: 10
  metrics:
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 70

Pausing and Resuming Rollouts

Useful when applying multiple changes at once:

kubectl rollout pause deployment/my-app
kubectl set image deployment/my-app my-app=myrepo/my-app:2.0
kubectl set env deployment/my-app ENVIRONMENT=production
kubectl rollout resume deployment/my-app

Common Commands

kubectl get deployments
kubectl describe deployment my-app
kubectl delete deployment my-app
kubectl rollout history deployment/my-app
kubectl rollout status deployment/my-app