* kube-apiserver: The external hostname no longer longer use the cloud provider API to select a default. It can be set explicitly using --external-hostname, if needed. If there is no default, AdvertiseAddress or os.Hostname() will be used, in that order. ([#56812](https://github.com/kubernetes/kubernetes/pull/56812), [@dims](https://github.com/dims))

- Kubelet config file will be backed up to `/etc/kubernetes/tmp/` folder with `kubeadm-kubelet-config` append with a random suffix as the filename ([#114695](https://github.com/kubernetes/kubernetes/pull/114695), [@chendave](https://github.com/chendave)) [SIG Cluster Lifecycle]
- Kubelet no longer creates certain legacy iptables rules by default.

*   Azure Load Balancer Auto Mode: Services can be annotated to allow auto selection of available load balancers and to provide specific availability sets that host the load balancers (for example, `service.beta.kubernetes.io/azure-load-balancer-mode=auto|as1,as2...`)

### **CLI**

#### **Kubectl**

you MUST read this before you upgrade)

- Kube-proxy's IPVS proxy mode no longer sets the net.ipv4.conf.all.route_localnet sysctl parameter. Nodes upgrading will have net.ipv4.conf.all.route_localnet set to 1 but new nodes will inherit the system default (usually 0). If you relied on any behavior requiring net.ipv4.conf.all.route_localnet, you must set ensure it is enabled as kube-proxy will no longer set it automatically. This change helps to further mitigate CVE-2020-8558. ([#92938]...

- Correct a reference to a not/no longer used kustomize subcommand in the documentation ([#82535](https://github.com/kubernetes/kubernetes/pull/82535), [@demobox](https://github.com/demobox))

* Fix metrics API group name in audit configuration ([#53493](https://github.com/kubernetes/kubernetes/pull/53493), [@piosz](https://github.com/piosz))
* Use separate client for leader election in scheduler to avoid starving leader election by regular scheduler operations. ([#53793](https://github.com/kubernetes/kubernetes/pull/53793), [@wojtek-t](https://github.com/wojtek-t))

- The deprecated flag `--lock-object-namespace` and `--lock-object-name` have been removed from kube-scheduler. Please use `--leader-elect-resource-namespace` and `--leader-elect-resource-name` or ComponentConfig instead to configure those parameters. ([#119130](https://github.com/kubernetes/kubernetes/pull/119130), [@SataQiu](https://github.com/SataQiu)) [SIG Scheduling]

- `Kubectl set resources` will no longer return an error if passed an empty change for a resource. `kubectl set subject` will no longer return an error if passed an empty change for a resource. ([#85490](https://github.com/kubernetes/kubernetes/pull/85490), [@sallyom](https://github.com/sallyom)) [SIG CLI]

* Performance test framework and basic tests for the IPAM controller, to simulate behavior of the four supported modes under lightly loaded and loaded conditions, where load is defined as the number of operations to perform as against the configured kubernetes. ([#61143](https://github.com/kubernetes/kubernetes/pull/61143), [@satyasm](https://github.com/satyasm))

- Kubernetes v1.13 moves support for Container Storage Interface to GA. As part of this move Kubernetes now supports CSI v1.0.0 and deprecates support for CSI 0.3 and older releases. Older CSI drivers must be updated to CSI 1.0 and moved to the new kubelet plugin registration directory in order to work with Kubernetes 1.15+. ([#71020](https://github.com/kubernetes/kubernetes/pull/71020), [@saad-ali](https://github.com/saad-ali))