Following dynamic provisioning, as you think about persistence systems – whether they are classic databases, key-value data stores, memory caches, or document-based datastores – it is common to want to have some manner of redundancy and failover. ReplicaSets and deployments go a fairly significant way to supporting some of that capability, especially with persistent volumes, but it would be greatly beneficial to these systems to have them more fully integrated with Kubernetes, so that we can leverage Kubernetes to handle the life cycle and coordination of these systems. A starting point for this effort is Stateful Sets, which act similarly to a deployment and ReplicaSet in that they manage a group of pods.
Stateful Sets differ from the other systems as they also support each pod having a stable, unique identity and specific ordered scaling, both up and down. Stateful Sets are relatively new in Kubernetes, first appearing in Kubernetes 1.5, and moving into beta in version 1.9...
