Merge pull request kubernetes-sigs#7228 from neoaggelos/feat/stdin-source

🌱 support clusterctl generate cluster with templates from stdin

Author: k8s-ci-robot

cmd/clusterctl/client/cluster/template.go

@@ -19,6 +19,7 @@ package cluster
 import (
 	"context"
 	"encoding/base64"
+	"io"
 	"net/http"
 	"net/url"
 	"os"
@@ -129,6 +130,14 @@ func (t *templateClient) GetFromURL(templateURL, targetNamespace string, skipTem
 }
 
 func (t *templateClient) getURLContent(templateURL string) ([]byte, error) {
+	if templateURL == "-" {
+		b, err := io.ReadAll(os.Stdin)
+		if err != nil {
+			return nil, errors.Wrapf(err, "failed to read stdin")
+		}
+		return b, nil
+	}
+
 	rURL, err := url.Parse(templateURL)
 	if err != nil {
 		return nil, errors.Wrapf(err, "failed to parse %q", templateURL)

cmd/clusterctl/client/cluster/template_test.go

@@ -307,6 +307,12 @@ func Test_templateClient_GetFromURL(t *testing.T) {
 	path := filepath.Join(tmpDir, "cluster-template.yaml")
 	g.Expect(os.WriteFile(path, []byte(template), 0600)).To(Succeed())
 
+	// redirect stdin
+	saveStdin := os.Stdin
+	defer func() { os.Stdin = saveStdin }()
+	os.Stdin, err = os.Open(path)
+	g.Expect(err).NotTo(HaveOccurred())
+
 	type args struct {
 		templateURL         string
 		targetNamespace     string
@@ -338,6 +344,16 @@ func Test_templateClient_GetFromURL(t *testing.T) {
 			want:    template,
 			wantErr: false,
 		},
+		{
+			name: "Get from stdin",
+			args: args{
+				templateURL:         "-",
+				targetNamespace:     "",
+				skipTemplateProcess: false,
+			},
+			want:    template,
+			wantErr: false,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

cmd/clusterctl/cmd/generate_cluster.go

@@ -124,7 +124,7 @@ func init() {
 
 	// flags for the url source
 	generateClusterClusterCmd.Flags().StringVar(&gc.url, "from", "",
-		"The URL to read the workload cluster template from. If unspecified, the infrastructure provider repository URL will be used")
+		"The URL to read the workload cluster template from. If unspecified, the infrastructure provider repository URL will be used. If set to '-', the workload cluster template is read from stdin.")
 
 	// flags for the config map source
 	generateClusterClusterCmd.Flags().StringVar(&gc.configMapName, "from-config-map", "",

docs/book/src/clusterctl/commands/generate-cluster.md

@@ -69,9 +69,10 @@ clusterctl generate cluster my-cluster --kubernetes-version v1.16.3 \
 Also following flags are available `--from-config-map-namespace` (defaults to current namespace) and `--from-config-map-key`
 (defaults to `template`).
 
-#### GitHub or local file system folder
+#### GitHub, local file system folder or standard input
 
-Use the `--from` flag to read cluster templates stored in a GitHub repository or in a local file system folder; e.g.
+Use the `--from` flag to read cluster templates stored in a GitHub repository, in a local file system folder,
+or from the standard input; e.g.
 
 ```bash
 clusterctl generate cluster my-cluster --kubernetes-version v1.16.3 \
@@ -85,6 +86,13 @@ clusterctl generate cluster my-cluster --kubernetes-version v1.16.3 \
    --from ~/my-template.yaml > my-cluster.yaml
 ```
 
+or
+
+```bash
+cat ~/my-template.yaml | clusterctl generate cluster my-cluster --kubernetes-version v1.16.3 \
+    --from - > my-cluster.yaml
+```
+
 ### Variables
 
 If the selected cluster template expects some environment variables, the user should ensure those variables are set in advance.