- New "field_validation_request_duration_seconds" metric, measures how long requests take, indicating the value of the fieldValidation query parameter and whether or not server-side field validation is enabled on the apiserver ([#109120](https://github.com/kubernetes/kubernetes/pull/109120), [@kevindelgado](https://github.com/kevindelgado))...

- Kubelet: added log for volume metric collection taking too long ([#107490](https://github.com/kubernetes/kubernetes/pull/107490), [@pacoxu](https://github.com/pacoxu))

- Fixed a bug where startupProbe stopped working after a container's first restart ([#101093](https://github.com/kubernetes/kubernetes/pull/101093), [@wzshiming](https://github.com/wzshiming)) [SIG Node]
- Fixed port-forward memory leak for long-running and heavily used connections. ([#99839](https://github.com/kubernetes/kubernetes/pull/99839), [@saschagrunert](https://github.com/saschagrunert)) [SIG API Machinery and Node]

#### CustomResourceDefinition OpenAPI Publishing

OpenAPI specs for native types have long been served at /openapi/v2, and they are consumed by a number of components, notably kubectl client-side validation, kubectl explain and OpenAPI based client generators.

With Kubernetes 1.15 as beta, OpenAPI schemas are also published for CRDs, as long as their schemas are structural.

- `watch.Until` now works for long durations. ([#67350](https://github.com/kubernetes/kubernetes/pull/67350), [@tnozicka](https://github.com/tnozicka))

- Fix clearing of rate-limiter for the queue of checks for cleaning stale pod disruption conditions. 
  The bug could result in the PDB synchronization updates firing too often or the pod disruption cleanups taking too long to happen. ([#114780](https://github.com/kubernetes/kubernetes/pull/114780), [@mimowo](https://github.com/mimowo)) [SIG Apps]

  is beta but disabled by default. ([#120198](https://github.com/kubernetes/kubernetes/pull/120198), [@pacoxu](https://github.com/pacoxu))
- `kubectl` will not support the `/swagger-2.0.0.pb-v1` endpoint that has been long deprecated. ([#119410](https://github.com/kubernetes/kubernetes/pull/119410), [@Jefftree](https://github.com/Jefftree))
- `scheduler`: handling of unschedulable pods because a `ResourceClass` is missing

* Fixed GlusterFS volumes taking too long to time out ([#48709](https://github.com/kubernetes/kubernetes/pull/48709), [@jsafrane](https://github.com/jsafrane))