- Kube-apiserver adds two new alpha metrics `conversion_webhook_request_total` and `conversion_webhook_duration_seconds` that allow users to monitor requests to CRD conversion webhooks, split by result, and failure_type (In case of failure). ([#118292](https://github.com/kubernetes/kubernetes/pull/118292), [@cchapla](https://github.com/cchapla)) [SIG API Machinery, Architecture...

* The webhook admission plugin now works even if the API server and the nodes are in two separate networks,for example, in GKE.
The webhook admission plugin now lets the webhook author use the DNS name of the service as the CommonName when generating the server cert for the webhook.
Action required:

- `apiserver_admission_webhook_admission_duration_seconds` buckets have been expanded, 25s is now the largest bucket size to match the webhook default timeout. ([#115802](https://github.com/kubernetes/kubernetes/pull/115802), [@logicalhan](https://github.com/logicalhan)) [SIG API Machinery and Instrumentation]

- `discovery.k8s.io/v1beta1`...

Kubernetes 1.19 / go 1.15. Serving certificates used by admission webhooks, custom resource conversion webhooks, and aggregated API servers must now include valid Subject Alternative Names. If you are running Kubernetes 1.22 with `GODEBUG=x509ignoreCN=0` set, check the `apiserver_kube_aggregator_x509_missing_san_total` and `apiserver_webhooks_x509_missing_san_total` metrics for non-zero values to see if the API server is connecting to webhooks or aggregated API servers using certificates that will be considered...

- New metrics: `apiserver_kube_aggregator_x509_missing_san_total` and `apiserver_webhooks_x509_missing_san_total`. This metric measures a number of connections to webhooks/aggregated API servers that use certificates without Subject Alternative Names. It being non-zero is a warning sign that these connections will stop functioning in the future since Golang is going to deprecate...

- Added a new metric `webhook_fail_open_count` to monitor webhooks that fail to open. ([#107171](https://github.com/kubernetes/kubernetes/pull/107171), [@ltagliamonte-dd](https://github.com/ltagliamonte-dd))

- Kube-apiserver: Authorization webhooks now report the following metrics:
  - apiserver_authorization_webhook_evaluations_total
  - apiserver_authorization_webhook_duration_seconds
  - apiserver_authorization_webhook_evaluations_fail_open_total ([#123639](https://github.com/kubernetes/kubernetes/pull/123639), [@liggitt](https://github.com/liggitt))

- Allow expansion of ephemeral volumes ([#109987](https://github.com/kubernetes/kubernetes/pull/109987), [@gnufied](https://github.com/gnufied)) [SIG Node and Storage]
- Apiserver: fixed audit of loading more than one webhooks. ([#110145](https://github.com/kubernetes/kubernetes/pull/110145), [@sxllwx](https://github.com/sxllwx))

- Added support for CEL expressions to `v1alpha1 AuthorizationConfiguration` webhook `matchConditions`. ([#121223](https://github.com/kubernetes/kubernetes/pull/121223), [@ritazh](https://github.com/ritazh))