* In-place node upgrades to this release from versions 1.7.14, 1.8.9, and 1.9.4 are not supported if using subpath volumes with PVCs.  Such pods should be drained from the node first.

* The minimum supported version of Docker is now 1.11; if you are using Docker 1.10 or below, be sure to upgrade Docker before upgrading Kubernetes. ([#57845](https://github.com/kubernetes/kubernetes/pull/57845), [@yujuhong](https://github.com/yujuhong))

  
  vSphere releases less than 67u3 are deprecated as of v1.21. Please consider upgrading vSphere to 67u3 or above. vSphere CSI Driver requires minimum vSphere 67u3.
  
  VM Hardware version less than 15 is deprecated as of v1.21. Please consider upgrading the Node VM Hardware version to 15 or above. vSphere CSI Driver recommends Node VM's Hardware version set to at least vmx-15.

*   The Go version was upgraded from go1.8.3 to **go1.9.2** ([#51375](https://github.com/kubernetes/kubernetes/pull/51375),[ @cblecker](https://github.com/cblecker))
    *   The minimum supported go version bumps to 1.9.1. ([#55301](https://github.com/kubernetes/kubernetes/pull/55301),[ @xiangpengzhao](https://github.com/xiangpengzhao))

- Kubelet allows pods to use the `net.ipv4.ip_local_reserved_ports` sysctl by default and the minimal kernel version is 3.16; Pod Security admission allows this sysctl in v1.27+ versions of the baseline and restricted policies. ([#115374](https://github.com/kubernetes/kubernetes/pull/115374), [@pacoxu](https://github.com/pacoxu)) [SIG Auth, Network...

- The default Go version was updated to 1.11.2. ([#70665](https://github.com/kubernetes/kubernetes/pull/70665))
- The minimum supported Go version was updated to 1.11.2 ([#69386](https://github.com/kubernetes/kubernetes/pull/69386))
- CNI is unchanged at v0.6.0 since Kubernetes 1.10 ([#51250](https://github.com/kubernetes/kubernetes/pull/51250))

### Bug or Regression

- Fixed a bug where a high churn of events was causing master instability by reducing the maximum number of objects (events) attached to a single etcd lease. ([#100452](https://github.com/kubernetes/kubernetes/pull/100452), [@mborsz](https://github.com/mborsz)) [SIG API Machinery and Instrumentation]

* [Federation][kubefed]: Use StorageClassName for etcd pvc ([#46323](https://github.com/kubernetes/kubernetes/pull/46323), [@marun](https://github.com/marun))
* Restrict active deadline seconds max allowed value to be maximum uint32 ([#46640](https://github.com/kubernetes/kubernetes/pull/46640), [@derekwaynecarr](https://github.com/derekwaynecarr))

- VSphere releases less than 7.0u2 are deprecated as of v1.24. Please consider upgrading vSphere to 7.0u2 or above. vSphere CSI Driver requires minimum vSphere 7.0u2.

  
  The CSI Migration feature for vSphere Volume also requires minimum vSphere vCenter/ESXi Version to be 7.0u1 and minimum HW Version to be VM version 15.
  

- The `EmptyDir` memory backed volumes are sized as the minimum of pod allocatable memory on a host and an optional explicit user provided value. ([#101048](https://github.com/kubernetes/kubernetes/pull/101048), [@dims](https://github.com/dims))