- Added `kubeadm alpha certs certificate-key` command to generate secure random key to use on `kubeadm init --experimental-upload-certs` ([#77848](https://github.com/kubernetes/kubernetes/pull/77848), [@yagonobre](https://github.com/yagonobre))

### **Scheduling**

*   Taint key `unreachable` is now in GA.
*   Taint key `notReady` is changed to `not-ready`, and is also now in GA.
*   These changes are automatically updated for taints. Tolerations for these taints must be updated manually. Specifically, you must:

- kube-controller-manager currently needs a writable `--cert-dir` (default is `/var/run/kubernetes`) for generating self-signed certificates, when no `--tls-cert-file` or `--tls-private-key-file` are provided.
- The `system:kube-controller-manager` ClusterRole lacks permission to `get` the `configmap` extension-apiserver-authentication. kube-controller-manager errors if run with a service account bound to the clusterrole.

- Kubeadm: during execution of the "check expiration" command, treat the etcd CA as external if there is a missing etcd CA key file (etcd/ca.key) and perform the proper validation on certificates signed by the...

    * --docker_only
    * --docker-tls
    * --docker-tls-ca
    * --docker-tls-cert
    * --docker-tls-key
    * --enable_load_reader
    * --event_storage_age_limit
    * --event_storage_event_limit
    * --global_housekeeping_interval
    * --google-json-key
    * --log_cadvisor_usage
    * --machine_id_file
    * --storage_driver_user
    * --storage_driver_password

* The `kube-cloud-controller-manager` flag `--service-account-private-key-file` was non-functional and is now deprecated. ([#50289](https://github.com/kubernetes/kubernetes/pull/50289), [@liggitt](https://github.com/liggitt))
    * The `kube-cloud-controller-manager` flag `--use-service-account-credentials` is now honored consistently, regardless of whether `--service-account-private-key-file` was specified.

* kubectl create secret has a new option --from-env-file that populates a secret from file which follows a key=val format for each line.

- Kubeadm: during execution of the `certs check-expiration` command, treat the etcd CA as external if there is a missing etcd CA key file (etcd/ca.key) and perform the proper validation on certificates signed by the etcd CA....

- kube-controller-manager
  - The deprecated `--insecure-experimental-approve-all-kubelet-csrs-for-group` flag has been removed.
- kubelet
  - The deprecated `--google-json-key` flag has been removed. Remove the `--google-json-key` flag from kubelet invocations before upgrading. ([#69354](https://github.com/kubernetes/kubernetes/pull/69354), [@yujuhong](https://github.com/yujuhong))

  * You can remove the "old" taints (stored internally as annotations) at any time after the upgrade by doing `kubectl annotate nodes <node name> scheduler.alpha.kubernetes.io/taints-` (note the minus at the end, which means "delete the taint with this key")