feat: ske kubeconfig create merge kubeconfig into the default kubeconfig file

Signed-off-by: Javier Vela <fjvela@gmail.com>

Author: fjvela

docs/stackit_ske_kubeconfig_create.md

@@ -1,14 +1,17 @@
 ## stackit ske kubeconfig create
 
-Creates a kubeconfig for an SKE cluster
+Updates the kubeconfig setup for an SKE cluster.
 
 ### Synopsis
 
-Creates a kubeconfig for a STACKIT Kubernetes Engine (SKE) cluster.
+Update a kubeconfig for a STACKIT Kubernetes Engine (SKE) cluster.
+
+By default, the kubeconfig information of the SKE cluster is merged into the default kubeconfig file of the current user. If the kubeconfig file doesn't exist, a new one will be created.
+
+You can change the default kubeconfig destination by specifying a custom filepath with the --filepath flag.
 
-By default the kubeconfig is created in the .kube folder, in the user's home directory. The kubeconfig file will be overwritten if it already exists.
-You can override this behavior by specifying a custom filepath with the --filepath flag.
 An expiration time can be set for the kubeconfig. The expiration time is set in seconds(s), minutes(m), hours(h), days(d) or months(M). Default is 1h.
+
 Note that the format is <value><unit>, e.g. 30d for 30 days and you can't combine units.
 
 ```

internal/cmd/ske/kubeconfig/create/create.go

@@ -83,7 +83,7 @@ func NewCmd(p *print.Printer) *cobra.Command {
 			}
 
 			if !model.AssumeYes && !model.DisableWriting {
-				prompt := fmt.Sprintf("Are you sure you want to create a kubeconfig for SKE cluster %q? This will OVERWRITE your current kubeconfig file, if it exists.", model.ClusterName)
+				prompt := fmt.Sprintf("Are you sure you want to update your kubeconfig for SKE cluster %q? This will update your kubeconfig file. \n If it the kubeconfig file doesn´t exists, it will create a new one.", model.ClusterName)
 				err = p.PromptForConfirmation(prompt)
 				if err != nil {
 					return err
@@ -137,10 +137,11 @@ func NewCmd(p *print.Printer) *cobra.Command {
 			}
 
 			if !model.DisableWriting {
-				err = skeUtils.WriteConfigFile(kubeconfigPath, kubeconfig)
+				err = skeUtils.MergeKubeConfig(kubeconfigPath, kubeconfig)
 				if err != nil {
 					return fmt.Errorf("write kubeconfig file: %w", err)
 				}
+				p.Outputf("\nSet kubectl context to %s with: kubectl config use-context %s\n", model.ClusterName, model.ClusterName)
 			}
 
 			return outputResult(p, model, kubeconfigPath, respKubeconfig, respLogin)
@@ -260,7 +261,7 @@ func outputResult(p *print.Printer, model *inputModel, kubeconfigPath string, re
 		if respKubeconfig != nil {
 			expiration = fmt.Sprintf(", with expiration date %v (UTC)", *respKubeconfig.ExpirationTimestamp)
 		}
-		p.Outputf("Created kubeconfig file for cluster %s in %q%s\n", model.ClusterName, kubeconfigPath, expiration)
+		p.Outputf("Updated kubeconfig file for cluster %s in %q%s\n", model.ClusterName, kubeconfigPath, expiration)
 
 		return nil
 	}

internal/pkg/services/ske/utils/utils.go

@@ -9,6 +9,7 @@ import (
 	"strconv"
 
 	"github.com/stackitcloud/stackit-cli/internal/pkg/utils"
+	"k8s.io/client-go/tools/clientcmd"
 
 	"github.com/stackitcloud/stackit-sdk-go/core/oapierror"
 	"github.com/stackitcloud/stackit-sdk-go/services/ske"
@@ -246,6 +247,45 @@ func ConvertToSeconds(timeStr string) (*string, error) {
 	return utils.Ptr(strconv.FormatUint(result, 10)), nil
 }
 
+// Merge new Kubeconfig into existing Kubeconfig. If it doesn´t exits, creates a new one
+func MergeKubeConfig(pathDestionationKubeConfig, contentNewKubeConfig string) error {
+	if contentNewKubeConfig == "" {
+		return fmt.Errorf("no data to merge. the new kubeconfig is empty")
+	}
+
+	newConfig, err := clientcmd.Load([]byte(contentNewKubeConfig))
+	if err != nil {
+		return fmt.Errorf("error loading new kubeconfig: %w", err)
+	}
+
+	// if the destionation kubeconfig does not exist, create a new one
+	if _, err := os.Stat(pathDestionationKubeConfig); os.IsNotExist(err) {
+		return WriteConfigFile(pathDestionationKubeConfig, contentNewKubeConfig)
+	}
+
+	existingConfig, err := clientcmd.LoadFromFile(pathDestionationKubeConfig)
+	if err != nil {
+		return fmt.Errorf("error loading existing kubeconfig: %w", err)
+	}
+
+	for name, authInfo := range newConfig.AuthInfos {
+		existingConfig.AuthInfos[name] = authInfo
+	}
+	for name, context := range newConfig.Contexts {
+		existingConfig.Contexts[name] = context
+	}
+	for name, cluster := range newConfig.Clusters {
+		existingConfig.Clusters[name] = cluster
+	}
+
+	err = clientcmd.WriteToFile(*existingConfig, pathDestionationKubeConfig)
+	if err != nil {
+		return fmt.Errorf("error writing merged kubeconfig: %w", err)
+	}
+
+	return nil
+}
+
 // WriteConfigFile writes the given data to the given path.
 // The directory is created if it does not exist.
 func WriteConfigFile(configPath, data string) error {