Cross-namespace communication in Kubernetes - Mini Project: Build & Apply

Cross-namespace communication

📖 Scenario: You are working with Kubernetes namespaces to organize your applications. You want to allow a pod in one namespace to communicate with a service in another namespace.

🎯 Goal: Set up two namespaces with a service in one namespace and a pod in another namespace that can communicate with that service using the full DNS name.

📋 What You'll Learn

Create two namespaces named frontend and backend

Deploy a simple backend service in the backend namespace

Deploy a pod in the frontend namespace that can access the backend service using the full DNS name

Verify communication by printing the response from the backend service

💡 Why This Matters

🌍 Real World

In real Kubernetes clusters, teams use namespaces to separate environments or projects. Services in one namespace often need to talk to services in another namespace.

💼 Career

Understanding cross-namespace communication is essential for Kubernetes administrators and DevOps engineers to design secure and scalable applications.

1

Create namespaces

Create two namespaces called frontend and backend using kubectl commands.

Kubernetes

# Create the frontend namespace
# Create the backend namespace

Need a hint?

Use kubectl create namespace frontend and kubectl create namespace backend to create the namespaces.

2

Deploy backend service

Deploy a simple backend pod and service in the backend namespace. Use the image hashicorp/http-echo with arguments -text=Hello from backend. Name the pod backend-pod and the service backend-service.

Kubernetes

kubectl create namespace frontend
kubectl create namespace backend
# Deploy backend pod and service in backend namespace

Need a hint?

Use kubectl run with --namespace=backend to create the pod, then kubectl expose pod to create the service.

3

Deploy frontend pod with curl

Deploy a pod named frontend-pod in the frontend namespace using the image curlimages/curl. This pod will be used to test communication to the backend service.

Kubernetes

kubectl create namespace frontend
kubectl create namespace backend
kubectl run backend-pod --image=hashicorp/http-echo --restart=Never --namespace=backend -- -text="Hello from backend"
kubectl expose pod backend-pod --port=5678 --target-port=5678 --name=backend-service --namespace=backend
# Deploy frontend pod in frontend namespace

Need a hint?

Use kubectl run frontend-pod --image=curlimages/curl --restart=Never --namespace=frontend -- sleep 3600 to create a pod that stays running.

4

Test cross-namespace communication

Use kubectl exec to run a curl command inside frontend-pod in the frontend namespace. Access the backend service at http://backend-service.backend.svc.cluster.local:5678 and print the response.

Kubernetes

kubectl create namespace frontend
kubectl create namespace backend
kubectl run backend-pod --image=hashicorp/http-echo --restart=Never --namespace=backend -- -text="Hello from backend"
kubectl expose pod backend-pod --port=5678 --target-port=5678 --name=backend-service --namespace=backend
kubectl run frontend-pod --image=curlimages/curl --restart=Never --namespace=frontend -- sleep 3600
# Run curl inside frontend-pod to access backend-service

Need a hint?

Use kubectl exec -n frontend frontend-pod -- curl -s http://backend-service.backend.svc.cluster.local:5678 to test communication.