Blue-Green Deployments on Kubernetes

Blue-green deployment keeps two identical environments and switches traffic atomically. On Kubernetes, you achieve this with two Deployments and a Service selector flip.

Architecture

Deployment Steps

Database migrations

Blue-green with schema changes requires backward-compatible migrations or expand-contract patterns. Both versions may run simultaneously during the switch.

Kubernetes Manifest Pattern

# green deployment (currently active)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-green
spec:
  replicas: 3
  selector:
    matchLabels:
      app: api
      version: green
  template:
    metadata:
      labels:
        app: api
        version: green
---
apiVersion: v1
kind: Service
metadata:
  name: api
spec:
  selector:
    app: api
    version: green   # flip to blue after validation
  ports:
    - port: 80

CI/CD Integration

deploy:blue:
  stage: deploy
  script:
    - kubectl apply -f k8s/blue/
    - ./scripts/smoke-test.sh https://blue.internal.example.com
  environment:
    name: blue
 
switch:production:
  stage: deploy
  when: manual
  script:
    - kubectl patch service api -p '{"spec":{"selector":{"version":"blue"}}}'

When to Use Blue-Green

Scenario	Fit
Stateless APIs	Excellent
Instant rollback needed	Excellent
Stateful apps with sticky sessions	Requires care
Cost-sensitive	Higher (2x resources during switch)

Conclusion

Blue-green trades resource cost for simplicity and instant rollback. Pair it with automated smoke tests in CI before flipping the Service selector.

Blue-Green Deployments on Kubernetes

Architecture

Deployment Steps

Kubernetes Manifest Pattern

CI/CD Integration

When to Use Blue-Green

Conclusion

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