Blue-Green Deployment in Kubernetes

💡 Quick Answer: deployments

The Problem

This is a fundamental Kubernetes topic that engineers search for frequently. A comprehensive reference with production-ready examples saves hours of trial and error.

The Solution

Native Blue-Green with Service Selector

# Blue deployment (current production)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-blue
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web
      version: blue
  template:
    metadata:
      labels:
        app: web
        version: blue
    spec:
      containers:
        - name: web
          image: my-app:v1
---
# Green deployment (new version)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-green
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web
      version: green
  template:
    metadata:
      labels:
        app: web
        version: green
    spec:
      containers:
        - name: web
          image: my-app:v2
---
# Switch traffic by updating selector
apiVersion: v1
kind: Service
metadata:
  name: web
spec:
  selector:
    app: web
    version: blue     # ← Change to "green" to switch
  ports:
    - port: 80

# Deploy green alongside blue
kubectl apply -f web-green.yaml

# Test green (port-forward to green directly)
kubectl port-forward deployment/web-green 8080:80

# Switch traffic: blue → green
kubectl patch svc web -p '{"spec":{"selector":{"version":"green"}}}'

# Instant rollback: green → blue
kubectl patch svc web -p '{"spec":{"selector":{"version":"blue"}}}'

# Clean up old version after confirming
kubectl delete deployment web-blue

Blue-Green vs Canary vs Rolling

graph TD
    A[Service: web] -->|selector: version=blue| B[Blue: v1 - 3 pods]
    C[Green: v2 - 3 pods] -->|Ready and tested| D[Switch selector]
    D --> E[Service: web → version=green]
    E --> C
    F[Problem?] --> G[Switch back to blue - instant]

Frequently Asked Questions

Blue-green vs rolling update?

Blue-green: run both versions fully, switch traffic instantly, instant rollback. Costs 2x resources during deployment. Rolling update: gradually replace pods, lower resource cost, slower rollback.

Best Practices

• Start with the simplest configuration that meets your needs
• Test changes in staging before production
• Use kubectl describe and events for troubleshooting
• Document your decisions for the team

Key Takeaways

• This is essential Kubernetes knowledge for production operations
• Follow the principle of least privilege and minimal configuration
• Monitor and iterate based on real-world behavior
• Automation reduces human error and improves consistency