Blue‑Green Deployment with Host and Path‑Based Routing in Kubernetes

Kubernetes is an open‑source container orchestration system that simplifies application deployment, scaling, and management. This article provides a step‑by‑step tutorial for performing a blue‑green deployment with host‑ and path‑based routing.

Prerequisites

Kubernetes cluster

kubectl command‑line tool

Docker image of the application to be deployed

Step 1: Create Namespace

kubectl create namespace blue-green-deployment

Step 2: Create Deployments

Create the blue deployment manifest (blue-deployment.yaml):

# blue-deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: demoapp-blue
  labels:
    app: demoapp
    env: blue
spec:
  replicas: 3
  selector:
    matchLabels:
      app: demoapp
      env: blue
  template:
    metadata:
      labels:
        app: demoapp
        env: blue
    spec:
      containers:
      - name: demo
        image: demoapp:v1.0
        ports:
        - containerPort: 80

Apply the blue deployment:

kubectl apply -f blue-deployment.yaml -n blue-green-deployment

Create a similar green deployment manifest (green-deployment.yaml) and apply it.

Step 3: Create Service

Create the service manifest (service.yaml):

# service.yaml
apiVersion: v1
kind: Service
metadata:
  name: demoapp-service
spec:
  selector:
    app: demoapp
  ports:
  - name: http
    port: 80
    targetPort: 80
  type: LoadBalancer

Apply the service:

kubectl apply -f service.yaml -n blue-green-deployment

Get the external IP address of the service:

kubectl get service demoapp-service -n blue-green-deployment

Step 4: Define Routing Rules

Update the service manifest to include session affinity and traffic policy, then apply it:

# service.yaml (updated)
apiVersion: v1
kind: Service
metadata:
  name: demoapp-service
spec:
  selector:
    app: demoapp
  ports:
  - name: http
    port: 80
    targetPort: 80
  type: LoadBalancer
  sessionAffinity: ClientIP
  externalTrafficPolicy: Local
  loadBalancerSourceRanges:
  - 0.0.0.0/0

kubectl apply -f service.yaml -n blue-green-deployment

Step 5: Host and Path‑Based Routing

Extend the service manifest with an Ingress resource that routes traffic based on host and path:

# service.yaml (with Ingress)
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: demoapp-ingress
spec:
  rules:
  - host: "demoapp.example.com"
    http:
      paths:
      - path: /blue
        backend:
          service:
            name: demoapp-blue
            port:
              number: 80
      - path: /green
        backend:
          service:
            name: demoapp-green
            port:
              number: 80

kubectl apply -f service.yaml -n blue-green-deployment

Step 6: Execute Blue‑Green Switch

With both blue and green deployments running, switch traffic from the blue deployment to the green deployment by updating the Ingress rules or service selectors.

Step 7: Update Green Deployment

Create a new green deployment manifest (green-deployment-v2.yaml) with the updated application image and apply it:

# green-deployment-v2.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: demoapp-green
  labels:
    app: demoapp
    env: green
spec:
  replicas: 3
  selector:
    matchLabels:
      app: demoapp
      env: green
  template:
    metadata:
      labels:
        app: demoapp
        env: green
    spec:
      containers:
      - name: myapp
        image: myapp:v2.0
        ports:
        - containerPort: 80

kubectl apply -f green-deployment-v2.yaml -n blue-green-deployment

Step 8: Update Service to Route to Green

Modify the service selector to point to the green deployment and re‑apply:

# service.yaml (selector updated to env: green)
apiVersion: v1
kind: Service
metadata:
  name: demoapp-service
spec:
  selector:
    app: demoapp
    env: green
  ports:
  - name: http
    port: 80
    targetPort: 80
  type: LoadBalancer

kubectl apply -f service.yaml -n blue-green-deployment

Step 9: Verify Deployment

Access the application using the external IP address in a web browser to confirm that the new version is serving traffic.

Step 10: Rollback (If Needed)

If problems arise, roll back by changing the service selector back to the blue deployment and re‑applying the service manifest:

# service.yaml (selector set to env: blue)
apiVersion: v1
kind: Service
metadata:
  name: demoapp-service
spec:
  selector:
    app: demoapp
    env: blue
  ports:
  - name: http
    port: 80
    targetPort: 80
  type: LoadBalancer

kubectl apply -f service.yaml -n blue-green-deployment

These steps provide a complete workflow for performing a blue‑green deployment on Kubernetes with host‑ and path‑based routing, enabling zero‑downtime releases and easy rollback.