### StatefulSet

* Fix zone placement heuristics so that multiple mounts in a StatefulSet pod are created in the same zone ([#40910](https://github.com/kubernetes/kubernetes/pull/40910), [@justinsb](https://github.com/justinsb))

* StatefulSet: The deprecated `pod.alpha.kubernetes.io/initialized` annotation for interrupting the StatefulSet Pod management is now ignored. StatefulSets with this annotation set to `true` or with no value will behave just as they did in previous versions. Dormant StatefulSets with the annotation set to `false` will become active after upgrading.

### **Application Deployment**
#### StatefulSet
* [beta] StatefulSet supports [RollingUpdate](https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#rolling-updates) and [OnDelete](https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#on-delete) update strategies.

* PetSet has been renamed to StatefulSet.
  If you have existing PetSets, **you must perform extra migration steps** both

*   StatefulSet controller now creates a label for each Pod in a StatefulSet. The label is `statefulset.kubernetes.io/pod-name`, where `pod-name` = the name of the Pod. This allows users to create a Service per Pod to expose a connection to individual Pods. ([#55329](https://github.com/kubernetes/kubernetes/pull/55329),[...

- `StatefulSetAutoDeletePVC` feature gate promoted to beta. ([#116501](https://github.com/kubernetes/kubernetes/pull/116501), [@mattcary](https://github.com/mattcary))
- `StatefulSet` names must be DNS labels, rather than subdomains. Any `StatefulSet`
  which took advantage of subdomain validation (by having dots in the name) can't
  possibly have worked, because we eventually set `pod.spec.hostname` from the `StatefulSetName`,

- Fixes a panic in kube-controller-manager handling StatefulSet objects when revisionHistoryLimit is negative ([#129325](https://github.com/kubernetes/kubernetes/pull/129325), [@ardaguclu](https://github.com/ardaguclu)) [SIG Apps]

- Fix nil pointer dereference in azure cloud provider ([#85975](https://github.com/kubernetes/kubernetes/pull/85975), [@ldx](https://github.com/ldx)) [SIG Cloud Provider]
- Fix regression in statefulset conversion which prevents applying a statefulset multiple times. ([#87706](https://github.com/kubernetes/kubernetes/pull/87706), [@liggitt](https://github.com/liggitt)) [SIG Apps and Testing]

- Fix regression in statefulset conversion which prevented applying a statefulset multiple times. ([#87721](https://github.com/kubernetes/kubernetes/pull/87721), [@liggitt](https://github.com/liggitt)) [SIG Apps and Testing]

- Validation now requires new StatefulSets with a `.spec.serviceName` field value to pass DNS1123 validation. Previously created StatefulSets with an invalid `.spec.serviceName` field value could not create any pods, and should be deleted.