* CustomResourceDefinitions: OpenAPI v3 validation schemas containing `$ref`references are no longer permitted. Before upgrading, ensure CRD definitions do not include those `$ref` fields. ([#58438](https://github.com/kubernetes/kubernetes/pull/58438), [@carlory](https://github.com/carlory))

### Other notable changes

* CustomResourceDefinitions: OpenAPI v3 validation schemas containing `$ref`references are no longer permitted (valid references could not be constructed previously because property ids were not permitted either). Before upgrading, ensure CRD definitions do not include those `$ref` fields. ([#58438](https://github.com/kubernetes/kubernetes/pull/58438), [@carlory](https://github.com/carlory))

- The `kubernetes.io/created-by` annotation is deprecated and will be removed in version 1.9.
  Use [ControllerRef](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/api-machinery/controller-ref.md) instead to determine which controller, if any, owns an object.

 - The `batch/v2alpha1.CronJob` is deprecated in favor of `batch/v1beta1`.

- This code change fixes the bug that UDP services would trigger unnecessary LoadBalancer updates. The root cause is that a field not working for non-TCP protocols is considered.
  ref: https://github.com/kubernetes-sigs/cloud-provider-azure/pull/1090 ([#107981](https://github.com/kubernetes/kubernetes/pull/107981), [@lzhecheng](https://github.com/lzhecheng))

* PodDisruptionBudget now uses [ControllerRef](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/api-machinery/controller-ref.md) to make the right decisions about Pod eviction even if the built in application controllers have overlapping selectors.

### **Security**
#### Admission Control