Certified Kubernetes Application Developer (CKAD) Study Guide, 2nd Edition

Chapter 21. Services

In “Using a Pod’s IP Address for Network Communication”, we learned that you can communicate with a Pod by its IP address. A restart of a Pod will automatically assign a new virtual cluster IP address. Therefore, other parts of your system cannot rely on the Pod’s IP address if they need to talk to one another.

Building a microservices architecture, where each of the components runs in its own Pod with the need to communicate with each other through a stable network interface, requires a different primitive, the Service.

The Service implements an abstraction layer on top of Pods, assigning a fixed virtual IP fronting all the Pods with matching labels, and that virtual IP is called Cluster IP. This chapter will focus on the ins and outs of Services, and most importantly the exposure of Pods inside and outside of the cluster based on their declared type.

Accessing a Service in minikube

Accessing Services of type NodePort and LoadBalancer in minikube requires special handling. Refer to the documentation for detailed instructions.

Coverage of Curriculum Objectives

This chapter addresses the following curriculum objective:

• Provide and troubleshoot access to applications via Services

Working with Services

In a nutshell, Services provide discoverable names and load balancing to a set of Pods. The Service remains agnostic from IP addresses with the help of the Kubernetes DNS control-plane component, an aspect we’ll discuss in “Discovering the Service by DNS ...