code: func PerformControlPlaneUpgrade(flags *applyFlags, client clientset.Interface, waiter apiclient.Waiter, internalcfg *kubeadmapi.InitConfiguration) error {
  
  	// OK, the cluster is hosted using static pods. Upgrade a static-pod hosted cluster
  	fmt.Printf("[upgrade/apply] Upgrading your Static Pod-hosted control plane to version %q...\n", internalcfg.KubernetesVersion)
  
  	if flags.dryRun {
  		return DryRunStaticPodUpgrade(internalcfg)
  	}
  
  	// Don't save etcd backup directory if etcd is HA, as this could cause corruption
  	return PerformStaticPodUpgrade(client, waiter, internalcfg, flags.etcdUpgrade, flags.renewCerts)
  }
docs: // PerformControlPlaneUpgrade actually performs the upgrade procedure for the cluster of your type (self-hosted or static-pod-hosted)