- `kubeadm`: turned on feature gate `MergeCLIArgumentsWithConfig` to merge the config from flag and config file, otherwise, if the flag `--ignore-preflight-errors` is set from the CLI, then the value from config file will be ignored. ([#119946](https://github.com/kubernetes/kubernetes/pull/119946), [@chendave](https://github.com/chendave))

* Created a new `dryRun` query parameter for mutating endpoints. If the parameter is set, then the query will be rejected, as the feature is not implemented yet. This will allow forward compatibility with future clients; otherwise, future clients talking with older apiservers might end up modifying a resource even if they include the `dryRun` query parameter. ([#63557](https://github.com/kubernetes/kubernetes/pull/63557), [@apelisse](https://github.com/apelisse))

- Reduce default NodeStatusReportFrequency to 5 minutes. With this change, periodic node status updates will be send every 5m if node status doesn't change (otherwise they are still send with 10s).

Some upgrade methods might upgrade etcd from 3.0 to 3.1 automatically when you upgrade from Kubernetes 1.8, unless you specify otherwise. Because [etcd does not support downgrading](https://coreos.com/etcd/docs/latest/upgrades/upgrade_3_1.html), you'll need to either remain on etcd 3.1 or restore from a backup if you want to downgrade back to Kubernetes 1.8.

- Bumped `ProcMountType` feature to on by default beta ([#130798](http...

of this feature (with one caveat -- see below), in which you specify affinity requests using Pod annotations, in 1.6 by including `AffinityInAnnotations=true` in `--feature-gates`, such as `--feature-gates=FooBar=true,AffinityInAnnotations=true`. Otherwise, you must modify your PodSpecs that currently use the `scheduler.alpha.kubernetes.io/affinity` annotation on Pod, to instead use the `affinity` field in the PodSpec. Support for the annotation will be removed in a future release, so we encourage...

- etcd2 as a backend is deprecated and support will be removed in Kubernetes 1.13.
- The --storage-versions flag of kube-apiserver is now deprecated. This flag should be omitted to ensure the default storage versions are used. Otherwise the cluster is not safe to upgrade to a version newer than 1.12. This flag will be removed in 1.13. ([#68080](https://github.com/kubernetes/kubernetes/pull/68080), [@caesarxuchao](https://github.com/caesarxuchao)) Courtesy of SIG API Machinery

  New Pods that have a node- or cluster-critical priority are prohibited from accessing swap on Linux,
  even if your cluster and node configuration could otherwise allow this. ([#125277](https://github.com/kubernetes/kubernetes/pull/125277), [@iholder101](https://github.com/iholder101)) [SIG Node and Testing]

JSON API clients should tolerate `null` values for such fields, and treat `null` and `[]` as equivalent in meaning unless specifically documented otherwise for a particular field. ([#44593](https://github.com/kubernetes/kubernetes/pull/44593))

  - true/strict - perform validation and error the request on any invalid fields in the ojbect. It will attempt to perform server-side validation if it is enabled on the apiserver, otherwise it will fall back to client-side validation.