implement namespace specific cluster operations

This commit allows running "create", "delete" and "apply" kedge
subcommands with an optional "-n/--namespace" flag, which
specifies the Kubernetes namespace to perform the given operation
on.

The ExecuteKubectl() function in pkg/cmd/kubernetes.go is
refactored to accept multiple arguments to pass to "kubectl"
instead of just one, as before.

Fixes kedgeproject#93

cmd/apply.go

@@ -25,15 +25,16 @@ import (
 
 // Variables
 var (
-	ApplyFiles []string
+	ApplyNamespace string
+	ApplyFiles     []string
 )
 
 // Represents the "apply" command
 var applyCmd = &cobra.Command{
 	Use:   "apply",
 	Short: "Apply a configuration to a resource on the Kubernetes cluster. This resource will be created if it doesn't exist yet.",
 	Run: func(cmd *cobra.Command, args []string) {
-		if err := pkgcmd.ExecuteKubectl(ApplyFiles, "apply"); err != nil {
+		if err := pkgcmd.ExecuteKubectl(ApplyFiles, "apply", "--namespace", ApplyNamespace); err != nil {
 			fmt.Println(err)
 			os.Exit(-1)
 		}
@@ -42,5 +43,6 @@ var applyCmd = &cobra.Command{
 
 func init() {
 	applyCmd.Flags().StringArrayVarP(&ApplyFiles, "files", "f", []string{}, "Specify files")
+	applyCmd.Flags().StringVarP(&ApplyNamespace, "namespace", "n", "default", "Kubernetes namespace to deploy your application to")
 	RootCmd.AddCommand(applyCmd)
 }

cmd/create.go

@@ -26,7 +26,8 @@ import (
 
 // Variables
 var (
-	CreateFiles []string
+	CreateNamespace string
+	CreateFiles     []string
 )
 
 // Represents the "create" command
@@ -38,7 +39,7 @@ var createCmd = &cobra.Command{
 			fmt.Println(err)
 			os.Exit(-1)
 		}
-		if err := pkgcmd.ExecuteKubectl(CreateFiles, "create"); err != nil {
+		if err := pkgcmd.ExecuteKubectl(CreateFiles, "create", "--namespace", CreateNamespace); err != nil {
 			fmt.Println(err)
 			os.Exit(-1)
 		}
@@ -48,5 +49,7 @@ var createCmd = &cobra.Command{
 func init() {
 	createCmd.Flags().StringArrayVarP(&CreateFiles, "files", "f", []string{}, "Specify files")
 	createCmd.MarkFlagRequired("files")
+	createCmd.Flags().StringVarP(&CreateNamespace, "namespace", "n", "default", "Kubernetes namespace to deploy your application to")
+
 	RootCmd.AddCommand(createCmd)
 }

cmd/delete.go

@@ -26,7 +26,8 @@ import (
 
 // Variables
 var (
-	DeleteFiles []string
+	DeleteNamespace string
+	DeleteFiles     []string
 )
 
 // Represents the "delete" command
@@ -38,7 +39,7 @@ var deleteCmd = &cobra.Command{
 			fmt.Println(err)
 			os.Exit(-1)
 		}
-		if err := pkgcmd.ExecuteKubectl(DeleteFiles, "delete"); err != nil {
+		if err := pkgcmd.ExecuteKubectl(DeleteFiles, "delete", "--namespace", DeleteNamespace); err != nil {
 			fmt.Println(err)
 			os.Exit(-1)
 		}
@@ -48,5 +49,6 @@ var deleteCmd = &cobra.Command{
 func init() {
 	deleteCmd.Flags().StringArrayVarP(&DeleteFiles, "files", "f", []string{}, "Specify files")
 	deleteCmd.MarkFlagRequired("files")
+	deleteCmd.Flags().StringVarP(&DeleteNamespace, "namespace", "n", "default", "Kubernetes namespace to delete your application from")
 	RootCmd.AddCommand(deleteCmd)
 }

pkg/cmd/kubernetes.go

@@ -28,7 +28,7 @@ import (
 	"github.com/pkg/errors"
 )
 
-func ExecuteKubectl(files []string, command string) error {
+func ExecuteKubectl(files []string, command ...string) error {
 
 	appData, err := getApplicationsFromFiles(files)
 	if err != nil {
@@ -53,7 +53,11 @@ func ExecuteKubectl(files []string, command string) error {
 				return errors.Wrap(err, "failed to marshal object")
 			}
 
-			cmd := exec.Command("kubectl", command, "-f", "-")
+			// We need to add "-f -" at the end of the command passed to us to
+			// pass the files.
+			// e.g. If the command is "apply --namespace staging", then the
+			// final command becomes "kubectl apply --namespace staging -f -"
+			cmd := exec.Command("kubectl", append(command, "-f", "-")...)
 
 			stdin, err := cmd.StdinPipe()
 			if err != nil {