- Using `--log-file` is known to be problematic in 1.15. This presents as things being logged multiple times to the same file. The behaviour and details of this issue, as well as some preliminary attempts at fixing it are documented [here](https://github.com/kubernetes/kubernetes/issues/78734#issuecomment-501372131)

- Sometimes, the scheduler incorrectly placed a pod in the "unschedulable" queue instead of the "backoff" queue. This happened when some plugin previously declared the pod as "unschedulable" and then in a later attempt encounters some other error. Scheduling of that pod then got delayed by up to five minutes, after which periodic flushing moved the pod back into the "active" queue. ([#120334](https://github.com/kubernetes/kubernetes/pull/120334),...

- Some command line errors (for example, "kubectl list" -> "unknown command") were printed as log message with escaped line breaks instead of a multi-line plain text, which made the error harder to read. ([#107044](https://github.com/kubernetes/kubernetes/pull/107044), [@pohly](https://github.com/pohly)) [SIG CLI and Testing]

Before updating to 1.9, you are strongly recommended to back up your etcd data. Consult the installation procedure you are using (kargo, kops, kube-up, kube-aws, kubeadm etc) for specific advice.

In some cases, for pure data validation and processing, you can get performance improvements of **20x** or more. This means 2,000% or more. 🤯

When you use **FastAPI**, there's a lot more going on, processing the request and response, handling dependencies, executing **your own code**, and particularly, **waiting for the network**. But you will probably still get some nice performance improvements just from the upgrade.

- Sometimes, the scheduler incorrectly placed a pod in the "unschedulable" queue instead of the "backoff" queue. This happened when some plugin previously declared the pod as "unschedulable" and then in a later attempt encounters some other error. Scheduling of that pod then got delayed by up to five minutes, after which periodic flushing moved the pod back into the "active" queue. ([#120334](https://github.com/kubernetes/kubernetes/pull/120334),...

* Fix a typo in prometheus-to-sd configuration, that drops some stackdriver metrics. ([#56473](https://github.com/kubernetes/kubernetes/pull/56473), [@loburm](https://github.com/loburm))

* Azure cloudprovider: Reduce the polling delay for all azure clients to 5 seconds. This should speed up some operations at the cost of some additional quota. ([#43699](https://github.com/kubernetes/kubernetes/pull/43699), [@colemickens](https://github.com/colemickens))

* add GRS, RAGRS storage account type support for azure disk ([#55931](https://github.com/kubernetes/kubernetes/pull/55931), [@andyzhangx](https://github.com/andyzhangx))
* Fix a typo in prometheus-to-sd configuration, that drops some stackdriver metrics. ([#56473](https://github.com/kubernetes/kubernetes/pull/56473), [@loburm](https://github.com/loburm))

  - [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)