Kubernetes Update Strategies: RollingUpdate vs Recreate vs Blue-Green

Strategy Comparison

RollingUpdate: maxSurge and maxUnavailable

spec:
  replicas: 10
  strategy:
    type: RollingUpdate
    rollingUpdate:
      # Max pods above desired during rollout
      maxSurge: 2         # Up to 12 pods temporarily

      # Max pods below desired (Unavailable) during rollout
      maxUnavailable: 0   # Never drop below 10 ready pods

Blue-Green with Kubernetes Services

# Deploy the green (new) version
kubectl apply -f deployment-green.yaml
# deployment-green.yaml has labels: version: green

# Wait for green to be fully ready
kubectl rollout status deployment/myapp-green

# Switch Service from blue to green (instant)
kubectl patch service myapp \
  -p '{"spec":{"selector":{"version":"green"}}}'

# Validate green is serving correctly
# ...smoke tests...

# Roll back instantly if needed:
kubectl patch service myapp \
  -p '{"spec":{"selector":{"version":"blue"}}}'

# Once validated, scale down or delete blue
kubectl scale deployment myapp-blue --replicas=0

Canary Deployments

Without a service mesh, approximate canary by replica ratio. 1 canary pod out of 10 total = 10% canary traffic (assuming equal-weight routing).

# Both deployments share the same Service selector label: app=myapp
# Service routes to both via label matching

# Stable: 9 replicas
apiVersion: apps/v1
kind: Deployment
metadata: {name: myapp-stable}
spec:
  replicas: 9
  selector:
    matchLabels: {app: myapp, version: stable}

---
# Canary: 1 replica = ~10% traffic
apiVersion: apps/v1
kind: Deployment
metadata: {name: myapp-canary}
spec:
  replicas: 1
  selector:
    matchLabels: {app: myapp, version: canary}

---
# Service selects on 'app: myapp' — matches BOTH deployments
kind: Service
spec:
  selector:
    app: myapp   # Routes to both stable and canary pods

Advanced: Argo Rollouts

Argo Rollouts replaces the standard Deployment controller with a custom resource that supports precise traffic splitting, automated analysis, and progressive delivery.

apiVersion: argoproj.io/v1alpha1
kind: Rollout
metadata:
  name: myapp
spec:
  replicas: 10
  strategy:
    canary:
      steps:
      - setWeight: 5      # 5% traffic to canary
      - pause: {duration: 5m}  # Wait 5 minutes
      - analysis:         # Run automated analysis
          templates:
          - templateName: success-rate
      - setWeight: 50     # Increase to 50%
      - pause: {}         # Manual approval gate
      - setWeight: 100    # Full promotion