kubeadm: include better details about v1alpha3 godocs

- update examples in v1alpha3/doc.go
- add docs link when printing `kubeadm config print-default`

cmd/kubeadm/app/apis/kubeadm/v1alpha3/doc.go

@@ -23,18 +23,32 @@ limitations under the License.
 // Some of these options are also available as command line flags, but
 // the preferred way to configure kubeadm is to pass a single YAML file with
 // multiple configuration types in with the --config option.
+// The configuration types should be separated by a line with `---`.
 //
-// kubeadm defines several configuration types:
+// kubeadm uses several API types:
 // * InitConfiguration
+// https://godoc.org/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1alpha3#InitConfiguration
 // * JoinConfiguration
+// https://godoc.org/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1alpha3#JoinConfiguration
 // * ClusterConfiguration
+// https://godoc.org/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1alpha3#ClusterConfiguration
+// * KubeProxyConfiguration
+// https://godoc.org/k8s.io/kube-proxy/config/v1alpha1#KubeProxyConfiguration
+// * KubeletConfiguration
+// https://godoc.org/k8s.io/kubelet/config/v1beta1#KubeletConfiguration
 //
-// InitConfiguration and JoinConfiguration cannot share a single YAML file,
-// however it is expected that InitConfiguration and ClusterConfiguration will
-// share a single YAML file.
+// For `kubeadm init` you can include the following types:
+//   InitConfiguration, ClusterConfiguration, KubeProxyConfiguration, KubeletConfiguration
 //
-//  A fully populated example of a single YAML file containing multiple
+// For `kubeadm join` you can include the following types:
+//   JoinConfiguration, KubeProxyConfiguration, KubeletConfiguration
+//
+// To print the default values for certain API type you can use:
+//   kubeadm config print-default --api-objects=<type1>,<type2>
+//
+//  Here is a fully populated example of a single YAML file containing multiple
 //  configuration types to be used during a `kubeadm init` run.
+//
 //	apiVersion: kubeadm.k8s.io/v1alpha3
 //	kind: InitConfiguration
 //	bootstrapTokens:
@@ -127,4 +141,5 @@ limitations under the License.
 //
 // TODO: The BootstrapTokenString object should move out to either k8s.io/client-go or k8s.io/api in the future
 // (probably as part of Bootstrap Tokens going GA). It should not be staged under the kubeadm API as it is now.
+//
 package v1alpha3 // import "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1alpha3"

cmd/kubeadm/app/cmd/config.go

@@ -98,9 +98,11 @@ func NewCmdConfigPrintDefault(out io.Writer) *cobra.Command {
 		Aliases: []string{"print-defaults"},
 		Short:   "Print the default values for a kubeadm configuration object.",
 		Long: fmt.Sprintf(dedent.Dedent(`
-			This command prints the default InitConfiguration object that is used for 'kubeadm init' and 'kubeadm upgrade',
+			This command prints objects such as the default InitConfiguration that is used for 'kubeadm init' and 'kubeadm upgrade',
 			and the default JoinConfiguration object that is used for 'kubeadm join'.
 
+			For documentation visit: https://godoc.org/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1alpha3
+
 			Note that sensitive values like the Bootstrap Token fields are replaced with silly values like %q in order to pass validation but
 			not perform the real computation for creating a token.
 		`), sillyToken),