- Scheduler's CycleState now embeds internal read/write locking inside its `Read()` and `Write()` functions. Meanwhile, `Lock()` and `Unlock()` function are removed. Scheduler plugin developers are now required to remove `CycleState#Lock()` and `CycleState#Unlock()`. Just simply use `Read()` and `Write()` as they're natively thread-safe now. ([#101542](https://github.com/kubernetes/kubernetes/pull/101542), [@Huang-Wei](http...

- Various controllers that write out IP address or CIDR values to API objects now
  ensure that they always write out the values in canonical form. ([#130101](https://github.com/kubernetes/kubernetes/pull/130101), [@danwinship](https://github.com/danwinship)) [SIG Apps, Network and Node]

* Check if container memory stats are available before accessing it ([#77656](https://github.com/kubernetes/kubernetes/pull/77656), [@yastij](https://github.com/yastij))
* client-go and kubectl no longer write cached discovery files with world-accessible file permissions ([#77874](https://github.com/kubernetes/kubernetes/pull/77874), [@yuchengwu](https://github.com/yuchengwu))

  * Log warning when invalid dir passed to `kubectl proxy --www` ([#44952](https://github.com/kubernetes/kubernetes/pull/44952), [@CaoShuFeng](https://github.com/CaoShuFeng))

  * Add `--write-config-to` flag to kube-proxy to allow users to write the default configuration settings to a file. ([#45908](https://github.com/kubernetes/kubernetes/pull/45908), [@ncdc](https://github.com/ncdc))

    * inside of which a write lock was intended to prevent races against
    * VM creation, but the usage of the sync.RWMutex type is incorrect,
    * plus is placed in a defer call so the locking is effectively
    * nonexistent.  This patch adds an anonymous function call inside
    * the loop to correctly handle acquiring the write lock with deferred

- Changed handling of `CustomResourceDefinitions` with unrecognized formats. Writing a schema with an unrecognized format now triggered a warning (the write was still accepted). ([#133136](https://github.com/kubernetes/kubernetes/pull/133136), [@yongruilin](https://github.com/yongruilin))

</p>

<pre>
type Reader interface {
	Read(p []byte) (n int, err error)
	Close() error
}

type Writer interface {
	Write(p []byte) (n int, err error)
	Close() error
}

// ReadWriter's methods are Read, Write, and Close.
type ReadWriter interface {
	Reader  // includes methods of Reader in ReadWriter's method set
	Writer  // includes methods of Writer in ReadWriter's method set

- When using `kubectl replace` (or the equivalent API call) on a Service, the caller no longer needs to do a read-modify-write cycle to fetch the allocated values for `.spec.clusterIP` and `.spec.ports[].nodePort`.  Instead the API server will automatically carry these forward from the original object when the new object does not specify them. ([#104673](https://github.co...

* When performing a GET then PUT, the kube-apiserver must write the canonical representation of the object to etcd if the current value does not match. That allows external agents to migrate content in etcd from one API version to another, across different storage types, or across varying encryption levels. This...

- Fixed a race condition on API server startup ensuring previously created webhook configurations are effective before the first write request is admitted. ([#95783](https://github.com/kubernetes/kubernetes/pull/95783), [@roycaihw](https://github.com/roycaihw)) [SIG API Machinery]