"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 `CustomResourceDefaulting` feature is promoted to beta and enabled by default. Defaults may be specified in structural schemas via the `apiextensions.k8s.io/v1` API. See https://kubernetes.io/docs/tasks/access-kubernetes-api/custom-resources/custom-resource-definitions/#specifying-a-structural-schema for details. ([#81872](https://github.com/kubernetes/kubernetes/pull/81872), [@sttts](https://github.com/sttts))

`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...

  - 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))

## Major themes

Kubernetes is developed by community members whose work is organized into
[Special Interest Groups](https://github.com/kubernetes/community/blob/master/sig-list.md), which provide the themes that guide their work. For the 1.9 release, these themes included:

### API Machinery

    - [Client Binaries](#client-binaries-15)
    - [Server Binaries](#server-binaries-15)
    - [Node Binaries](#node-binaries-15)
  - [Introduction to v1.8.0](#introduction-to-v180)
  - [Major Themes](#major-themes)
    - [SIG API Machinery](#sig-api-machinery)
    - [SIG Apps](#sig-apps)
    - [SIG Auth](#sig-auth)
    - [SIG Autoscaling](#sig-autoscaling)
    - [SIG Cluster Lifecycle](#sig-cluster-lifecycle)

  - 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))

  - [Urgent Upgrade Notes](#urgent-upgrade-notes)
    - [(No, really, you MUST do this before you upgrade)](#no-really-you-must-do-this-before-you-upgrade)
  - [Major Themes](#major-themes)
    - [SIG API Machinery](#sig-api-machinery)
    - [SIG Auth](#sig-auth)
    - [SIG CLI](#sig-cli)
    - [SIG Cluster Lifecycle](#sig-cluster-lifecycle)
    - [SIG Instrumentation](#sig-instrumentation)

	* Allow setting KubernetesClusterID or KubernetesClusterTag in combination with VPC. ([#42512](https://github.com/kubernetes/kubernetes/pull/42512), [@scheeles](https://github.com/scheeles))

	* Start recording cloud provider metrics for AWS ([#43477](https://github.com/kubernetes/kubernetes/pull/43477), [@gnufied](https://github.com/gnufied))