`UnversionedKubeletConfigMap` feature gate to Beta and enabled the feature by default. This implies that 1) for new clusters kubeadm will start using the `kube-system/kubelet-config` naming scheme for the kubelet ConfigMap and RBAC rules, instead of the legacy `kubelet-config-x.yy` naming. 2) during upgrade, kubeadm will only write the new scheme ConfigMap and RBAC objects. To disable the feature you can pass `UnversionedKubeletConfigMap: false` in the kubeadm config for new clusters. For upgrade on existing clusters...

- 'Container `preStop` and `postStart` lifecycle handlers using `httpGet` now
  honor the specified `scheme` and `headers` fields. This enables setting custom
  headers and changing the scheme to `HTTPS`, consistent with container
  startup/readiness/liveness probe capabilities. Lifecycle handlers configured
  with `scheme: HTTPS` that encounter errors indicating the endpoint is actually

### API-Machinery

* Fixed webhooks to use the scheme provided in clientConfig, instead of defaulting to http. ([#60943](https://github.com/kubernetes/kubernetes/pull/60943), [@jennybuckley](https://github.com/jennybuckley))

                                "content": {
                                    "application/json": {
                                        "schema": {
                                            "$ref": "#/components/schemas/HTTPValidationError"
                                        }
                                    }
                                },
                            },

beta and enabled by default. CustomResourceDefinitions with [structural schemas](https://github.com/kubernetes/enhancements/blob/master/keps/sig-api-machinery/20190425-structural-openapi.md) now publish schemas in the OpenAPI document served at `/openapi/v2`. CustomResourceDefinitions with non-structural schemas have a `NonStructuralSchema` condition added with details about what needs to be corrected in the validation schema. ([#77825](https://github.com/kubernetes/kubernetes/pull/77825), [@royc...

  - The `/swaggerapi/*` schema docs, deprecated since 1.7, have been removed in favor of the /openapi/v2 schema docs. ([#72924](https://github.com/kubernetes/kubernetes/pull/72924), [@liggitt](https://github.com/liggitt))

  - `spec.versions[*].schema.openAPIV3Schema` is now required when creating v1 CustomResourceDefinitions
  - `spec.preserveUnknownFields: true` is disallowed when creating v1 CustomResourceDefinitions; it must be specified within schema definitions as `x-kubernetes-preserve-unknown-fields: true`

* kube-apiserver: The `AdmissionConfiguration` type accepted by `--admission-control-config-file` has been promoted to `apiserver.config.k8s.io/v1` with no schema changes. ([#85098](https://github.com/kubernetes/kubernetes/pull/85098), [@liggitt](https://github.com/liggitt))...

  - The schema for the alpha `CSINodeInfo` CRD has been split into `spec` and `status` fields, and new fields `status.available` and `status.volumePluginMechanism` added. Clusters using the previous alpha schema must delete and recreate the CRD using the new schema. ([#70515](https://github.com/kubernetes/kubernetes/pull/70515), [@davidz627](https://github.com/davidz627))

- Removed deprecated command `kubectl stop`.

- Kubectl can now use http caching for the OpenAPI schema. The cache
  directory can be configured by passing the `--cache-dir` command line flag to kubectl.
  If set to an empty string, caching is disabled.

- Kubectl now performs validation against OpenAPI schema instead of Swagger 1.2. If
  OpenAPI is not available on the server, it falls back to the old Swagger 1.2.