✨ Add support to clusterctl for inserting workload kubeconfig into an existing kubeconfig file

Author: dmvolod

Diff for: cmd/clusterctl/cmd/get_kubeconfig.go

@@ -19,9 +19,11 @@ package cmd
 import (
 	"context"
 	"fmt"
+	"os"
 
 	"github.com/pkg/errors"
 	"github.com/spf13/cobra"
+	"k8s.io/client-go/tools/clientcmd"
 
 	clusterv1 "sigs.k8s.io/cluster-api/api/v1beta2"
 	"sigs.k8s.io/cluster-api/cmd/clusterctl/client"
@@ -32,6 +34,7 @@ type getKubeconfigOptions struct {
 	kubeconfig        string
 	kubeconfigContext string
 	namespace         string
+	intoKubeconfig    string
 }
 
 var gk = &getKubeconfigOptions{}
@@ -67,6 +70,8 @@ func init() {
 		"Path to the kubeconfig file to use for accessing the management cluster. If unspecified, default discovery rules apply.")
 	getKubeconfigCmd.Flags().StringVar(&gk.kubeconfigContext, "kubeconfig-context", "",
 		"Context to be used within the kubeconfig file. If empty, current context will be used.")
+	getKubeconfigCmd.Flags().StringVar(&gk.intoKubeconfig, "into-kubeconfig", "",
+		"Path to the kubeconfig file where the resulting kubeconfig will be inserted.")
 
 	// completions
 	getKubeconfigCmd.ValidArgsFunction = resourceNameCompletionFunc(
@@ -98,6 +103,35 @@ func runGetKubeconfig(workloadClusterName string) error {
 	if err != nil {
 		return err
 	}
+	if gk.intoKubeconfig != "" {
+		return intoKubeconfig(gk.intoKubeconfig, out)
+	}
+
 	fmt.Println(out)
 	return nil
 }
+
+func intoKubeconfig(path, kubeconfig string) error {
+	kubeconfigFile, err := os.CreateTemp("", "kubeconfig")
+	if err != nil {
+		return err
+	}
+	defer os.Remove(kubeconfigFile.Name())
+
+	if _, err = kubeconfigFile.WriteString(kubeconfig); err != nil {
+		return err
+	}
+	if err = kubeconfigFile.Close(); err != nil {
+		return err
+	}
+
+	rules := &clientcmd.ClientConfigLoadingRules{
+		Precedence: []string{path, kubeconfigFile.Name()},
+	}
+	config, err := rules.Load()
+	if err != nil {
+		return err
+	}
+
+	return clientcmd.WriteToFile(*config, rules.Precedence[0])
+}

Diff for: cmd/clusterctl/cmd/get_kubeconfig_test.go

@@ -0,0 +1,76 @@
+/*
+Copyright 2020 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cmd
+
+import (
+	_ "embed"
+	"os"
+	"path/filepath"
+	"testing"
+
+	. "github.com/onsi/gomega"
+)
+
+//go:embed testdata/existsing-kubeconfig.yaml
+var existingKubeconfig string
+
+//go:embed testdata/workload-kubeconfig.yaml
+var workloadKubeconfig string
+
+//go:embed testdata/joined-kubeconfig.yaml
+var joinedKubeconfig string
+
+func Test_intoKubeconfig(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	tt := []struct {
+		name     string
+		path     string
+		data     string
+		expected string
+	}{
+		{
+			name:     "inserting into empty kubeconfig",
+			path:     filepath.Join(tmpDir, "empty-kubeconfig"),
+			data:     "",
+			expected: workloadKubeconfig,
+		},
+		{
+			name:     "inserting into existing kubeconfig",
+			path:     filepath.Join(tmpDir, "existing-kubeconfig"),
+			data:     existingKubeconfig,
+			expected: joinedKubeconfig,
+		},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			g := NewWithT(t)
+			if tc.data != "" {
+				err := os.WriteFile(tc.path, []byte(tc.data), 0600)
+				g.Expect(err).ToNot(HaveOccurred())
+			}
+
+			err := intoKubeconfig(tc.path, workloadKubeconfig)
+			g.Expect(err).ToNot(HaveOccurred())
+
+			expected, err := os.ReadFile(tc.path)
+			g.Expect(err).ToNot(HaveOccurred())
+			g.Expect(string(expected)).To(Equal(tc.expected))
+		})
+	}
+}

Diff for: cmd/clusterctl/cmd/testdata/existsing-kubeconfig.yaml

@@ -0,0 +1,19 @@
+apiVersion: v1
+clusters:
+- cluster:
+    certificate-authority-data: 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
+    server: https://127.0.0.1:42341
+  name: kind-caaph-e2e
+contexts:
+- context:
+    cluster: kind-caaph-e2e
+    user: kind-caaph-e2e
+  name: kind-caaph-e2e
+current-context: kind-caaph-e2e
+kind: Config
+preferences: {}
+users:
+- name: kind-caaph-e2e
+  user:
+    client-certificate-data: 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
+    client-key-data: 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