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Service Types: ClusterIP vs NodePort

Hands-on example​

Assume:

  • A working Kubernetes cluster
  • kubectl is configured

Initial state​

No Services or Deployments exist.

kubectl get svc
kubectl get deployments
No resources found in default namespace.
No resources found in default namespace.

Step 1: Create a Deployment​

kubectl create deployment demo --image=nginx
deployment.apps/demo created

Verify the Pod.

kubectl get pods
NAME                    READY   STATUS    RESTARTS   AGE
demo-6f7c8d9f6b-abcde   1/1     Running   0          5s

Step 2: Expose as ClusterIP​

kubectl expose deployment demo --port=80 --target-port=80
service/demo exposed

Check the Service.

kubectl get svc
NAME   TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE
demo   ClusterIP   10.96.120.45   <none>        80/TCP    5s

What changed:

  • A ClusterIP Service was created

What did not change:

  • No external access exists

Step 3: Access ClusterIP from inside the cluster​

Run a temporary Pod.

kubectl run curl --image=curlimages/curl -it --rm --restart=Never -- sh

Inside the Pod:

curl http://demo
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
...

Exit the Pod.

Step 4: Change Service to NodePort​

kubectl patch svc demo -p '{"spec":{"type":"NodePort"}}'
service/demo patched

Check again.

kubectl get svc
NAME   TYPE       CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
demo   NodePort   10.96.120.45   <none>        80:30007/TCP   1m

What changed:

  • A node port was allocated

What did not change:

  • ClusterIP stayed the same
  • Pod selection stayed the same

Key observation​

  • NodePort adds external access but keeps ClusterIP
  • Do not use NodePort as a load balancer replacement