The purpose of StatefulSets is to provide some consistency and predictability to application deployments with stateful data. Thus far, we have deployed applications to the cluster, defining loose requirements around required resources such as compute and storage. The cluster has scheduled our workload on any node that can meet these requirements. While we can use some of these constraints to deploy in a more predictable manner, it will be helpful if we had a construct built to help us provide this consistency.

This is where StatefulSets come in. StatefulSets provide us first with numbered and reliable naming for both network access and storage claims. The pods themselves are named with the following convention, where N is from 0 to the number of replicas:

"Name of Set"-N

This means that a StatefulSet called db with three replicas will create the following pods:

db-0
db-1
db-2

This gives Kubernetes a way to associate network names and PersistentVolumes with specific pods. Additionally, it also serves to order the creation and termination of pods. Pod will be started from 0 to N and terminated from N to 0.