Lab 2.3: Confusion regarding NodePort service and Cluster IP

Hi @tianli,

Services are covered in detail in Chapter 7, but before reaching that chapter I may be able to provide some clarification:

• The EXTERNAL-IP property of the Service is not the Node IP, it is typically a Load Balancer's IP address, and it is populated for LoadBalancer type Services in Kubernetes clusters running as managed cloud services. We are running a self-managed cluster. If our node is configured to act as a Load Balancer, then its IP address may be assigned to EXTERNAL-IP. An example with additional details can be found here.
• You are correct, the Pod is assigned to one of the Nodes, but reviewing the "Pod-to-Pod Communication" page of the course should answer your question as to why a Pod running on any Node is accessible from either Node of the cluster.
• I am not sure, however, what is the "External Cluster IP" you are asking about. Did you find this in the course lectures or the lab exercises?

Regards,
-Chris

Hi @runnergeek,

I just had an interesting conversation with another student, and one of the topics was the same as your question:

• Q: Why the need for a ClusterIP service if pods are assigned their own unique private IP addresses and can communicate with each other over the pod-to-pod network?
• A: A pod is ephemeral, meaning that both the pod's name and pod's IP address may change several times during the lifecycle of a containerized application running in the pod. A permanent solution is a service exposing the pods of an application, offering a permanent access interface with a consistent name and a stable ClusterIP address that integrate with the cluster's internal DNS that helps to remove any discovery overhead and communication complexity between pods.

Regards,
-Chris