* The following deprecated flags were removed from `kube-controller-manager`:

  * `replication-controller-lookup-cache-size`
  * `replicaset-lookup-cache-size`
  * `daemonset-lookup-cache-size`

  Don't use these flags. Using deprecated flags causes the server to print a warning. Using a removed flag causes the server to abort the startup.

- Fix performance regression in scheduler caused by frequent metric lookup on critical code path. ([#117617](https://github.com/kubernetes/kubernetes/pull/117617), [@tosi3k](https://github.com/tosi3k)) [SIG Scheduling]

* Disable proxy to loopback and linklocal ([#71980](https://github.com/kubernetes/kubernetes/pull/71980), [@micahhausler](https://github.com/micahhausler))
* kube-scheduler: restores ability to run without authentication configuration lookup permissions ([#71755](https://github.com/kubernetes/kubernetes/pull/71755), [@liggitt](https://github.com/liggitt))

* kubelet: resolved hang/timeout issues when running large numbers of pods with unique configmap/secret references by reverting to 1.11 configmap/secret lookup behavior ([#74755](https://github.com/kubernetes/kubernetes/pull/74755), [@liggitt](https://github.com/liggitt))

resources, which represents the list of group aliases (e.g. "all") that every resource belongs to. ([#43338](https://github.com/kubernetes/kubernetes/pull/43338), [@fabianofranz](https://github.com/fabianofranz))

* `--service-account-lookup` now defaults to true, requiring the Secret API object containing the token to exist in order for a service account token to be valid. This enables service account tokens to be revoked by deleting the Secret object containing the token. ([#44071]...

- Fixed performance regression in scheduler caused by frequent metric lookup on critical code path. ([#117594](https://github.com/kubernetes/kubernetes/pull/117594), [@tosi3k](https://github.com/tosi3k))

- `client-go`, using log level 9, traces the following events of a HTTP request:
      - DNS lookup
      - TCP dialing
      - TLS handshake
      - Time to get a connection from the pool

* Performs validation (when applying for example) against OpenAPI schema rather than Swagger 1.0. ([#51364](https://github.com/kubernetes/kubernetes/pull/51364), [@apelisse](https://github.com/apelisse))
* Make all e2e tests lookup image to use from a centralized place. In that centralized place, add support for multiple platforms. ([#49457](https://github.com/kubernetes/kubernetes/pull/49457), [@mkumatag](https://github.com/mkumatag))

- Fixed performance regression in scheduler caused by frequent metric lookup on critical code path. ([#116441](https://github.com/kubernetes/kubernetes/pull/116441), [@alculquicondor](https://github.com/alculquicondor)) [SIG Scheduling]

- Hostnames are now converted to lowercase before being used for node lookups in the kubernetes-worker charm. ([#65487](https://github.com/kubernetes/kubernetes/pull/65487), [@dshcherb](https://github.com/dshcherb))