- The validation of `replicas` field in the ReplicationController `/scale` subresource has been migrated to declarative validation.
  If the `DeclarativeValidation` feature gate is enabled, mismatches with existing validation are reported via metrics.

- Migrated validation in `resource.k8s.io` to declarative validation.
  When the `DeclarativeValidation` feature gate is enabled, mismatches with existing validation are reported via metrics.

- The `DeclarativeValidation` feature gate is enabled by default. When enabled, mismatches with existing hand written validation is reported via metrics.

- The Pod API field `.spec.schedulingGates[*].name` now requires qualified names (like `example.com/mygate`), matching validation for names of `.spec.readinessGates[*].name`. Any uses of the alpha scheduling gate feature prior to 1.27 that do not match that validation must be renamed or deleted before upgrading to 1.27. ([#115821](https://github.com/kubernetes/kubernetes/pull/115821), [@lianghao208](https://github.com/lianghao208)) [SIG Apps...

Service Level Indicators (SLIs) and Service Level Objectives (SLOs) for the system.
Here's the release [scalability validation report].

[SIG Scalability]: https://github.com/kubernetes/community/tree/master/sig-scalability
[scalability validation report]: https://github.com/kubernetes/sig-release/blob/master/releases/release-1.8/scalability_validation_report.md

### SIG Scheduling

    *   Make crictl command more user friendly and add more subcommands.
    *   Integrate with CRI verbose option to provide extra debug information.
    *   Update CRI to kubernetes v1.9.
    *   Bug fixes in validation test suites.

that workloads (e.g. Deployments, DaemonSets, etc.) which used `PersistentDisk` volumes were using them in read-only mode.  This validation provided very little value at relatively host implementation cost, and will no longer be validated.  If this is a problem for a specific use-case, please set the `SkipReadOnlyValidationGCE` gate to false to re-enable the validation, and file a Kubernetes bug with details. ([#121083](https://github.com/kubernetes/kubernetes/pull/121083), [@thockin](https://github.com/thockin))...

  
  If `username.expression` used 'claims.email', then 'claims.email_verified' must have been used in `username.expression` or `extra[*].valueExpression` or `claimValidationRules[*].expression`. An example claim validation rule expression that matches the validation automatically applied when `username.claim` is set to 'email' is 'claims.?email_verified.orValue(true) == true'.
   ([#123737](https://github.com/kubernetes/kubernetes/pull/123737), [@enj](https://github.com/enj))

- Fixed EndpointSlice port name validation to match Endpoint port name validation (allowing port names longer than 15 characters) ([#84481](https://github.com/kubernetes/kubernetes/pull/84481), [@robscott](https://github.com/robscott))

- Dynamic Resource Allocation (DRA): client-side validation of a ResourceHandle would have accepted a missing DriverName, whereas server-side validation then would have raised an error. ([#124075](https://github.com/kubernetes/kubernetes/pull/124075), [@pohly](https://github.com/pohly))