code: func CheckClusterHealth(client clientset.Interface, ignoreChecksErrors sets.String) error {
  	fmt.Println("[upgrade] Making sure the cluster is healthy:")
  
  	healthChecks := []preflight.Checker{
  		&healthCheck{
  			name:   "APIServerHealth",
  			client: client,
  			f:      apiServerHealthy,
  		},
  		&healthCheck{
  			name:   "ControlPlaneNodesReady",
  			client: client,
  			f:      controlPlaneNodesReady,
  		},
  		// TODO: Add a check for ComponentStatuses here?
  	}
  
  	healthChecks = append(healthChecks, &healthCheck{
  		name:   "StaticPodManifest",
  		client: client,
  		f:      staticPodManifestHealth,
  	})
  
  	return preflight.RunChecks(healthChecks, os.Stderr, ignoreChecksErrors)
  }
docs: // CheckClusterHealth makes sure:
  // - the API /healthz endpoint is healthy
  // - all control-plane Nodes are Ready
  // - (if self-hosted) that there are DaemonSets with at least one Pod for all control plane components
  // - (if static pod-hosted) that all required Static Pod manifests exist on disk