Running Stateful Applications with Kubernetes

In this chapter, we will learn how to run stateful applications on Kubernetes. Kubernetes takes a lot of work out of our hands by automatically starting and restarting pods across the cluster nodes as needed, based on complex requirements and configurations such as namespaces, limits, and quotas. But when pods run storage-aware software, such as databases and queues, relocating a pod can cause the system to break. First, we'll explore the essence of stateful pods and why they are much more complicated to manage in Kubernetes. We will look at a few ways to manage the complexity, such as shared environment variables and DNS records. In some situations, a redundant in-memory state, a DaemonSet, or persistent storage claims can do the trick. The main solution that Kubernetes promotes for state-aware pods is the StatefulSet (previously called PetSet) resource, which allows us to manage an indexed collection of pods with stable properties...