What is the purpose of a StatefulSet in Kubernetes?

The purpose of a StatefulSet in Kubernetes is to provide persistent identifiers for stateful applications. StatefulSets are designed specifically for deploying and managing stateful applications, where each instance of the application (Pod) requires a unique, stable identity that persists across rescheduling and scaling events.

This functionality is crucial for applications that maintain state, such as databases or other services that rely on consistent storage. In a StatefulSet, each Pod gets a unique name and stable network identity, along with persistent storage, which allows stateful applications to function correctly despite changes in the environment. The Pods in a StatefulSet are not interchangeable as they have their own identities (like persistent storage volumes) and retain their state, which distinguishes them from a standard Deployment which manages stateless applications.

Thus, the capability of maintaining stable identifiers and persistent storage makes StatefulSets essential for managing applications that require state to function properly.