- Promoted the `CRDValidationRatcheting` feature gate to beta and made it enabled by default.
   ([#121461](https://github.com/kubernetes/kubernetes/pull/121461), [@alexzielenski](https://github.com/alexzielenski))

- Made `apiextensions-apiserver` binary linking static (also affects the deb and rpm packages). ([#114226](https://github.com/kubernetes/kubernetes/pull/114226), [@saschagrunert](https://github.com/saschagrunert))

methods in generated clientsets, dynamic, metadata, and scale clients have been modified to accept `context.Context` as a first argument. Signatures of Create, Update, and Patch methods have been updated to accept CreateOptions, UpdateOptions and PatchOptions respectively. Signatures of Delete and DeleteCollection methods now accept DeleteOptions by value instead of by reference. Generated clientsets with the previous interface have been added in new "deprecated" packages to allow incremental migration...

* The shortcuts that were moved server-side in at least 1.9 have been removed from being hardcoded in kubectl. This means that the client-based restmappers have been moved to client-go, where everyone who needs them can have access. ([#63507](https://github.com/kubernetes/kubernetes/pull/63507), [@deads2k](https://github.com/deads2k))

- Kubeadm: external etcd endpoints passed in the `ClusterConfiguration` that have Unicode characters are no longer IDNA encoded (converted to Punycode). They are now just URL encoded as per Go's implementation of RFC-3986, have duplicate "/" removed from the URL paths, and passed like that directly to the `kube-apiserver` `--etcd-servers` flag. If you have etcd endpoints that have Unicode characters, it is advisable to encode them in advance with tooling that is fully IDNA compliant....

In 1.12, SIG Cluster lifecycle has focused on improving the user experience in kubeadm, by fixing a number of bugs and adding some new important features.

Here is a list of some of the changes that have been made to kubeadm:

- Kubeadm internal config has been promoted to `v1alpha3`:
  - `v1alpha1` has been removed.

  
  Action required for custom scheduler plugin developers:
  Plugins **have to** implement a QueueingHint for Pod/Update event if the rejection from them could be resolved by updating unscheduled Pods themselves.
  Example: suppose you develop a custom plugin that denies Pods that have a `schedulable=false` label. 

- Newly provisioned PVs by vSphere in-tree plugin will no longer have the beta FailureDomain label. vSphere volume plugin will start to have GA topology label instead. ([#102414](https://github.com/kubernetes/kubernetes/pull/102414), [@divyenpatel](https://github.com/divyenpatel)) [SIG Cloud Provider, Storage and Testing]

- It introduces a new scope name `VolumeAttributesClass`. 
  
  It matches all PVC objects that have the volume attributes class mentioned. 
  

* Azure: Container permissions for provisioned volumes have changed to private. If you have existing Azure volumes that were created by Kubernetes v1.6.0-v1.6.5, you should change the permissions on them manually. ([#47605](https://github.com/kubernetes/kubernetes/pull/47605), [@brendandburns](https://github.com/brendandburns))