Kubernetes Blue-Green Deployments

Our critical application requires a swift version upgrade without downtime

Table of Contents

1. Introduction to Kubernetes

2. Creating Deployments and Services

   • Creating Deployments

   • Creating Services

3. ClusterIP Services

4. NodePort Services

5. Comparing Endpoint IPs with Pods

6. References

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Summary

Our application is currently running on version one. The image used is the "httpd: alpine" image. We planned to update it to the latest version using the "nginx: alpine" image. The change needs to be implemented immediately, without any delays. Once the update is complete, the new requests should redirect to the container running with the version 2 "nginx" image.

Creating Deployments and Services

Create version 1 of our application with the deployment and service definition file given here.

Table of Contents

1. Introduction to Kubernetes

2. Creating Deployments and Services

   • Creating Deployments

   • Creating Services

3. ClusterIP Services

4. NodePort Services

5. Comparing Endpoint IPs with Pods

6. References

---

Summary

Our application is currently running on version one. The image used is the "httpd: alpine" image. We planned to update it to the latest version using the "nginx: alpine" image. The change needs to be implemented immediately, without any delays. Once the update is complete, the new requests should redirect to the container running with the version 2 "nginx" image.

Creating Deployments and Services

Create version 1 ( Blue ) of our application with the deployment and service definition file given here.

Creating deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: bluegreenv1
  name: blue
spec:
  replicas: 4
  selector:
    matchLabels:
      app: bluegreen
      version: appv1
  template:
    metadata:
      labels:
        app: bluegreen
        version: appv1
    spec:
      containers:
      - image: httpd:alpine
        name: httpd

Apply the Deployment:

kubectl create -f nginx-deploymentV1.yaml

Creating Services

Now let's create the Service that points to the bluegreen Deployment:

apiVersion: v1
kind: Service
metadata:
  labels:
    app: bluegreen
  name: bluegreen
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
    nodePort: Change the port based on your username # 30101
  selector:
    app: bluegreen
    version: appv1
  type: NodePort

Create the Service:

kubectl create -f nginx-service.yaml

Testing the Deployment and Service

1. Create a ubuntu pod:

   kubectl run ubuntu  --image=ubuntu  --restart=Never -- sleep 3600

2. Execute a curl command to check if the ClusterIP service is listening to the Nginx webpage:

   kubectl exec -it ubuntu  -- /bin/bash
   curl nginx-service
   # Expected output: The HTML content of the Nginx webpage
   

3. Use the node's IP address and the specified nodePort (e.g., 30080) to access the Nginx service externally:

   http://<node_ip>:30080

Creating new Deployment bluegreen-v2

Next, let's create a new Deployment bluegreen-v2 which uses image nginx:alpine with 4 replicas. Its Pods should have labels "app: bluegreen" and version: v2

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: bluegreenv2
  name: green
spec:
  replicas: 4
  selector:
    matchLabels:
      app: bluegreen
      version: appv2
  template:
    metadata:
      labels:
        app: bluegreen
        version: appv2
    spec:
      containers:
      - image: nginx:alpine
        name: nginx

Create the Deployment:

kubectl create -f nginx-deploymentV1.yaml

Modify the Service

Now let's modify the Service to points to the bluegreenv2 Deployment:

apiVersion: v1
kind: Service
metadata:
  labels:
    app: bluegreen
  name: bluegreen
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
    nodePort: Change the port based on your username # 30101
  selector:
    app: bluegreen
    version: appv2
  type: NodePort

Apply the change:

kubectl apply -f nginx-service.yaml

Testing the Deployment and Service

1. Create a ubuntu pod:

   kubectl run ubuntu --image=ubuntu --restart=Never -- sleep 3600

2. Execute a curl command to check if the ClusterIP service is listening to the Nginx webpage:

   kubectl exec -it ubuntu -- sh
   curl nginx-service
   # Expected output: The HTML content of the Nginx webpage
   

3. Use the node's IP address and the specified nodePort (e.g., 30080) to access the Nginx service externally:

   http://<node_ip>:30080

Comparing Endpoint IPs with Pods

• Endpoints represent the IP addresses of one or more Pods dynamically assigned to a Service.

1. First, let's assume we have two Pods associated with our Nginx Deployment. We'll use the following Pod names:

   • nginx-pod-1

   • nginx-pod-2

2. Now, let's retrieve the IP addresses of these Pods using the kubectl get pods -o wide command:

   $ kubectl get pods -o wide
   NAME           READY   STATUS    RESTARTS   AGE   IP            NODE
   nginx-pod-1    1/1     Running   0          5m    10.244.1.10   node-1
   nginx-pod-2    1/1     Running   0          5m    10.244.2.20   node-2

   In this example:

   • nginx-pod-1 has an IP address of 10.244.1.10.

   • nginx-pod-2 has an IP address of 10.244.2.20.

3. Let's get more information about the nginx-service using kubectl describe:

kubectl describe service nginx-service

This command will provide detailed information about the service, including its IP address, ports, and associated endpoints.

1. Next, let's check the Endpoints associated with our nginx-service using the kubectl get endpoints nginx-service command:

   $ kubectl get endpoints nginx-service
   NAME            ENDPOINTS                      AGE
   nginx-service   10.244.1.10:80,10.244.2.20:80   5m

   Here, the nginx-service has endpoints corresponding to both Pods:

   • 10.244.1.10:80 (associated with nginx-pod-1)

   • 10.244.2.20:80 (associated with nginx-pod-2)

2. Finally, we can compare the IP addresses from the Endpoints with the Pod IPs to verify that they match.

Remember that these IP addresses are internal to the cluster and are used for communication between services and Pods. The Service abstraction ensures seamless connectivity without exposing individual Pod IPs externally.

References

• Kubernetes Documentation

• My Blog