Kubernetes Deployment Strategies

apiVersion: apps/v1
kind: Deployment
metadata:
  name: api
spec:
  replicas: 4
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1        # 1 extra pod during update
      maxUnavailable: 0  # Never reduce below desired count
  template:
    spec:
      containers:
        - name: api
          image: my-api:v2.0
          readinessProbe:
            httpGet:
              path: /ready
              port: 3000
            periodSeconds: 5

Step 1: v1 v1 v1 v1 + v2 (new)    → 5 pods, waiting for v2 ready
Step 2: v1 v1 v1 v2               → v1 terminated after v2 ready
Step 3: v1 v1 v2 + v2 (new)       → repeat
Step 4: v1 v2 v2 v2
Step 5: v2 v2 v2 v2               → done

strategy:
  type: Recreate

Step 1: v1 v1 v1 v1 → all terminated
Step 2: (downtime)
Step 3: v2 v2 v2 v2 → all created

# Blue (current production)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-blue
  labels:
    version: blue
spec:
  replicas: 4
  selector:
    matchLabels:
      app: api
      version: blue
  template:
    metadata:
      labels:
        app: api
        version: blue
    spec:
      containers:
        - name: api
          image: my-api:v1.0
---
# Green (new version)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-green
  labels:
    version: green
spec:
  replicas: 4
  selector:
    matchLabels:
      app: api
      version: green
  template:
    metadata:
      labels:
        app: api
        version: green
    spec:
      containers:
        - name: api
          image: my-api:v2.0
---
# Service — switch by changing selector
apiVersion: v1
kind: Service
metadata:
  name: api
spec:
  selector:
    app: api
    version: blue   # ← Change to "green" to switch
  ports:
    - port: 80
      targetPort: 3000

# Test green
kubectl exec test-pod -- curl http://api-green:3000/health

# Switch production traffic
kubectl patch service api -p '{"spec":{"selector":{"version":"green"}}}'

# Instant rollback
kubectl patch service api -p '{"spec":{"selector":{"version":"blue"}}}'

# Stable: 9 replicas
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-stable
spec:
  replicas: 9
  selector:
    matchLabels:
      app: api
      track: stable
  template:
    metadata:
      labels:
        app: api
        track: stable
    spec:
      containers:
        - name: api
          image: my-api:v1.0
---
# Canary: 1 replica (~10% traffic)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-canary
spec:
  replicas: 1
  selector:
    matchLabels:
      app: api
      track: canary
  template:
    metadata:
      labels:
        app: api
        track: canary
    spec:
      containers:
        - name: api
          image: my-api:v2.0
---
# Service selects both
apiVersion: v1
kind: Service
metadata:
  name: api
spec:
  selector:
    app: api      # Matches both stable and canary
  ports:
    - port: 80
      targetPort: 3000

# Stable ingress
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: api-stable
spec:
  rules:
    - host: api.example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: api-stable
                port:
                  number: 80
---
# Canary ingress (10% traffic)
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: api-canary
  annotations:
    nginx.ingress.kubernetes.io/canary: "true"
    nginx.ingress.kubernetes.io/canary-weight: "10"
spec:
  rules:
    - host: api.example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: api-canary
                port:
                  number: 80

# View rollout history
kubectl rollout history deployment/api

# Rollback to previous
kubectl rollout undo deployment/api

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

# Check rollout status
kubectl rollout status deployment/api

# Pause/resume rollout
kubectl rollout pause deployment/api
kubectl rollout resume deployment/api