In this chapter, we covered stateful applications that use persistent volumes. Compared to ephemeral volumes, they have some pitfalls when an application restarts or a pod scales. In addition, persistent volume management on Kubernetes has been enhanced to make it easier, as you can see from tools such as StatefulSet and dynamic provisioning.

Furthermore, Jobs and CronJobs are special utilities for pods. Compared to deployment/ReplicaSets, this has a desired number of pods running, which is against Job's ideal situation in which the pods should be deleted once they finish their tasks. This kind of short-lived application can be managed by Kubernetes as well.

In Chapter 5, Cluster Administration and Extension, we will discuss the cluster administration such as authentication, authorization, and admission control. We will also introduce the Custom Resource Definition (CRD) that how to control Kubernetes object by your own code.