Kubernetes Deployment Strategies

Overview

Kubernetes provides powerful primitives for zero-downtime deployments. Understanding deployment strategies is essential for maintaining high availability in production.

Strategy Comparison

Strategy	Downtime	Risk	Rollback Speed	Resource Cost
Recreate	Yes	High	Fast	Low
Rolling Update	None	Medium	Medium	Low
Blue/Green	None	Low	Instant	2x
Canary	None	Very Low	Instant	Medium
A/B Testing	None	Low	Instant	Medium

Rolling Update (Default)

rolling-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app
  namespace: production
spec:
  replicas: 6
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 2        # Allow 2 extra pods during update
      maxUnavailable: 1  # At most 1 pod down at a time
  selector:
    matchLabels:
      app: web-app
  template:
    metadata:
      labels:
        app: web-app
        version: v2
    spec:
      containers:
        - name: web-app
          image: myapp:v2.1.0
          ports:
            - containerPort: 8080
          readinessProbe:
            httpGet:
              path: /healthz
              port: 8080
            initialDelaySeconds: 10
            periodSeconds: 5
            failureThreshold: 3
          livenessProbe:
            httpGet:
              path: /livez
              port: 8080
            initialDelaySeconds: 30
            periodSeconds: 10
          resources:
            requests:
              memory: "128Mi"
              cpu: "250m"
            limits:
              memory: "256Mi"
              cpu: "500m"

Warning

Always define readinessProbe. Without it, Kubernetes sends traffic to pods that aren't ready, causing 5xx errors during rollouts.

Blue/Green Deployment

Loading diagram…

blue-green.yaml

# Blue deployment (current production)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app-blue
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web-app
      slot: blue
  template:
    metadata:
      labels:
        app: web-app
        slot: blue
        version: v1
    spec:
      containers:
        - name: web-app
          image: myapp:v1.0.0

---
# Green deployment (new version)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app-green
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web-app
      slot: green
  template:
    metadata:
      labels:
        app: web-app
        slot: green
        version: v2
    spec:
      containers:
        - name: web-app
          image: myapp:v2.0.0

---
# Service — switch between blue/green by changing selector
apiVersion: v1
kind: Service
metadata:
  name: web-app-svc
spec:
  selector:
    app: web-app
    slot: green  # ← Change this to switch traffic
  ports:
    - port: 80
      targetPort: 8080

Switching Traffic

switch-traffic.sh

# Switch to green
kubectl patch service web-app-svc -p '{"spec":{"selector":{"slot":"green"}}}'

# Verify rollout
kubectl get pods -l slot=green

# If issues, instant rollback to blue
kubectl patch service web-app-svc -p '{"spec":{"selector":{"slot":"blue"}}}'

Canary Deployment

Deploy canary with 10% traffic

# Deploy canary (1 replica = 10% if main has 9)
kubectl apply -f canary-deployment.yaml

canary-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app-canary
spec:
  replicas: 1
  selector:
    matchLabels:
      app: web-app
      track: canary
  template:
    metadata:
      labels:
        app: web-app
        track: canary
    spec:
      containers:
        - name: web-app
          image: myapp:v2.0.0-beta

Monitor metrics for 30 minutes

# Watch error rate
kubectl top pods -l app=web-app
kubectl logs -l track=canary --tail=100 -f

Promote to full rollout

# If metrics look good, promote
kubectl set image deployment/web-app-main web-app=myapp:v2.0.0-beta
kubectl delete deployment web-app-canary

Rollback

rollback.sh

# Check rollout history
kubectl rollout history deployment/web-app

# Rollback to previous version
kubectl rollout undo deployment/web-app

# Rollback to specific revision
kubectl rollout undo deployment/web-app --to-revision=3

# Check rollout status
kubectl rollout status deployment/web-app