you must keep the following in mind:

* **JSON configuration files that contain fields with incorrect case will no longer be valid. You must correct these files before upgrading.** When specifying keys in JSON resource definitions during direct API server communication, the keys are case-sensitive. A bug introduced in Kubernetes 1.8 caused the API server to accept a request with incorrect case and coerce it to correct case, but this behaviour has been fixed in 1.11 and the API server...

    * If you are running E2E tests which require SSH keys and you utilize environment variables to override their location, you may need to modify the environment variable set. On all providers the environment variable override can now be either an absolute path to the key or a relative path (relative to ~/.ssh). Specifically the changes are:
    *  - Created new GCE_SSH_KEY allowing specification of SSH keys for gce, gke, and kubemark.

- Kubeadm: warn but do not error out on missing "ca.key" files for root CA, front-proxy CA and etcd CA, during "kubeadm join --control-plane" if the user has provided all certificates, keys and kubeconfig files which require signing with the given CA keys. ([#94988](https://github.com/kubernetes/kubernetes/pull/94988), [@neolit123](https://github.com/neolit123)) [SIG Cluster Lifecycle]

- The API server now re-uses data encryption keys while the kms v2 plugin key ID is stable.  Data encryption keys are still randomly generated on server start but an atomic counter is used to prevent nonce collisions. ([#116155](https://github.com/kubernetes/kubernetes/pull/116155), [@enj](https://github.com/enj))

- kubeadm still generates RSA keys when deploying a node, but also accepts ECDSA
keys if they already exist in the directory specified in the `--cert-dir` option. ([#76390](https://github.com/kubernetes/kubernetes/pull/76390), [@rojkov](https://github.com/rojkov))

- 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...

	// type of s is string
	// s == a[i]
	g(i, s)
}

var key string
var val interface{}  // element type of m is assignable to val
m := map[string]int{"mon":0, "tue":1, "wed":2, "thu":3, "fri":4, "sat":5, "sun":6}
for key, val = range m {
	h(key, val)
}
// key == last map key encountered in iteration
// val == map[key]

var ch chan Work = producer()
for w := range ch {
	doWork(w)
}

  * 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")

  - `--service-account-key-file`, set to one or more files containing one or more public keys used to verify tokens.

- Fixed a regression in default configurations, which enabled `PodDisruptionConditions`
  by default, that prevented the control plane's pod garbage collector from deleting
  pods that contained duplicated field keys (environmental variables with repeated keys or
  container ports). ([#121103](https://github.com/kubernetes/kubernetes/pull/121103), [@mimowo](https://github.com/mimowo))