- When registering with a 1.17+ API server, a CustomResourceDefinition conversion webhook can now request that only `v1` ConversionReview requests be sent to them. Previously, conversion webhooks were required to support receiving `v1beta1` ConversionReview requests as well for compatibility with API servers <= 1.15. ([#82707](https://github.com/kubernetes/kubernetes/pull/82707), [@liggitt...

  - `kube-apiserver` now only aggregates openapi schemas from `/openapi/v2` endpoints of aggregated API servers. The fallback to aggregate from `/swagger.json` has been removed. Ensure aggregated API servers provide schema information via `/openapi/v2` (available since v1.10). ([#73441](https://github.com/kubernetes/kubernetes/pull/73441), [@roycaihw](https://github.com/roycaihw))

* Introduced `--http2-max-streams-per-connection` command line flag on api-servers and set default to 1000 for aggregated API servers. ([#60054](https://github.com/kubernetes/kubernetes/pull/60054), [@MikeSpreitzer](https://github.com/MikeSpreitzer))

* Introduced `--http2-max-streams-per-connection` command line flag on api-servers and set default to 1000 for aggregated API servers. ([#60054](https://github.com/kubernetes/kubernetes/pull/60054), [@MikeSpreitzer](https://github.com/MikeSpreitzer))

* kube-apiserver now includes all registered API groups in discovery, including registered extension API group/versions for unavailable extension API servers. ([#66932](https://github.com/kubernetes/kubernetes/pull/66932), [@nilebox](https://github.com/nilebox))

* Introduced `--http2-max-streams-per-connection` command line flag on api-servers and set default to 1000 for aggregated API servers. ([#60054](https://github.com/kubernetes/kubernetes/pull/60054), [@MikeSpreitzer](https://github.com/MikeSpreitzer))

* Fix a string comparison bug in IPVS graceful termination where UDP real servers are not deleted. ([#78999](https://github.com/kubernetes/kubernetes/pull/78999), [@andrewsykim](https://github.com/andrewsykim))

- Fixed a bug where an API group's path was not unregistered from the API server's root paths when the group was deleted. ([#121283](https://github.com/kubernetes/kubernetes/pull/121283), [@tnqn](https://github.com/tnqn)) [SIG API Machinery and Testing]

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 invalid in Kubernetes 1.23+.

##...

- API server's deprecated `--experimental-encryption-provider-config` flag is now removed. Adapt your machinery to use the `--encryption-provider-config` flag that is available since v1.13. ([#108423](https://github.com/kubernetes/kubernetes/pull/108423), [@ialidzhikov](https://github.com/ialidzhikov))