lab: kube: add flag --version to create subcommand (#112)

cmd/kube_create.go

@@ -198,7 +198,11 @@ var kubeCreateCmd = &cobra.Command{
 			return err
 		}
 
-		kubernetesVersion, err := fetchKubernetesVersion()
+		requestedKubernetesVersion, err := cmd.Flags().GetString("version")
+		if err != nil {
+			return err
+		}
+		kubernetesVersion, err := fetchKubernetesVersion(requestedKubernetesVersion)
 		if err != nil {
 			return err
 		}
@@ -502,10 +506,26 @@ func (c *sshClient) scp(src, dst string) error {
 	return ioutil.WriteFile(dst, buf.Bytes(), 0600)
 }
 
-// fetchKubernetesVersion fetches the version from the latest file
+// fetchKubernetesVersion fetches the latest stable version from the official
+// release source, or if a specific version is requested checks if it actually
+// exists.
 //
 // https://godoc.org/github.com/kubernetes/kubernetes/cmd/kubeadm/app/util#KubernetesReleaseVersion
-func fetchKubernetesVersion() (string, error) {
+func fetchKubernetesVersion(requested string) (string, error) {
+	if requested != "" {
+		r, err := http.Head(fmt.Sprintf("https://dl.k8s.io/release/v%s/bin/linux/amd64/kubectl", requested))
+		if err != nil {
+			return "", err
+		}
+		defer r.Body.Close()
+
+		if r.StatusCode != http.StatusOK {
+			return "", fmt.Errorf("unable to find Kubernetes release for version %q", requested)
+		}
+
+		return requested, nil
+	}
+
 	r, err := http.Get("https://dl.k8s.io/release/stable.txt")
 	if err != nil {
 		return "", err
@@ -530,5 +550,6 @@ func init() {
 	kubeCreateCmd.PersistentFlags().BoolVarP(&kubeCreateDebug, "debug", "d", false, "debug mode on")
 	kubeCreateCmd.Flags().StringP("size", "s", "medium", "<name | id> "+
 		"(micro|tiny|small|medium|large|extra-large|huge|mega|titan|jumbo)")
+	kubeCreateCmd.Flags().StringP("version", "v", "", "install a specific Kubernetes version")
 	kubeCmd.AddCommand(kubeCreateCmd)
 }