* Allows extension API server to dynamically discover the requestheader CA certificate when the core API server doesn't use certificate based authentication for it's clients ([#66394](https://github.com/kubernetes/kubernetes/pull/66394), [@rtripat](https://github.com/rtripat))

    * Don't generate empty record for externalName service.
    * Add validation for upstreamNameserver port.
    * Update go version to 1.9.3.
* CRI: define the mount behavior when host path does not exist: runtime should report error if the host path doesn't exist ([#61460](https://github.com/kubernetes/kubernetes/pull/61460), [@feiskyer](https://github.com/feiskyer))

## Changelog since v1.26.0

## Known Issues

### The PreEnqueue extension point doesn't work for Pods going to activeQ through backoffQ

In v1.26.0, we've found the bug that the PreEnqueue extension point doesn't work for Pods going to activeQ through backoffQ. 
It doesn't affect any of the vanilla Kubernetes behavior, but, may break custom PreEnqueue plugins.

- When the cluster size is small and the scheduler doesn't get unscheduled Pods frequently, the scheduler doesn't try to reschedule Pods in some cases. ([#119784](https://github.com/kubernetes/kubernetes/pull/119784), [@sanposhiho](https://github.com/sanposhiho)) [SIG Scheduling and Testing]

## Dependencies

* Allows extension API server to dynamically discover the requestheader CA certificate when the core API server doesn't use certificate based authentication for it's clients ([#66394](https://github.com/kubernetes/kubernetes/pull/66394), [@rtripat](https://github.com/rtripat))

### Bug or Regression

- EndpointSlice Mirroring controller now cleans up managed EndpointSlices when a Service selector is added (#106135, @robscott) [SIG Apps, Network and Testing]
- Fix a bug that `--disabled-metrics` doesn't function well. (#106391, @Huang-Wei) [SIG API Machinery, Cluster Lifecycle and Instrumentation]
- Fix a panic in kubectl when creating secrets with an improper output type (#106354, @lauchokyip) [SIG CLI]

  - [Changelog since v1.18.17](#changelog-since-v11817)
  - [Important Security Information](#important-security-information)
    - [CVE-2021-25735: Validating Admission Webhook does not observe some previous fields](#cve-2021-25735-validating-admission-webhook-does-not-observe-some-previous-fields)
  - [Changes by Kind](#changes-by-kind-2)
    - [API Change](#api-change-1)
    - [Feature](#feature)
    - [Bug or Regression](#bug-or-regression-2)

- The extension API server can now dynamically discover the requestheader CA certificate when the core API server doesn't use certificate based authentication for it's clients. ([#66394](https://github.com/kubernetes/kubernetes/pull/66394), [@rtripat](https://github.com/rtripat))

### SIG Autoscaling

    * Action required:
    * Anyone who generated server cert for admission webhooks need to regenerate the cert. Previously, when generating server cert for the admission webhook, the CN value doesn't matter. Now you must set it to the DNS name of the webhook service, i.e., `<service.Name>.<service.Namespace>.svc`.

- Reduce default NodeStatusReportFrequency to 5 minutes. With this change, periodic node status updates will be send every 5m if node status doesn't change (otherwise they are still send with 10s).