feat: add a guard to prevent to start the migration when the targeted

label is the only one.

checks.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"context"
+
+	v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/kubernetes"
+)
+
+func isTheEditedLabelTheOnlyOne(
+	namespace string,
+	clientset *kubernetes.Clientset,
+	deploymentName string,
+	changingLabelKey string,
+) bool {
+	deployment, _ := clientset.AppsV1().Deployments(namespace).Get(context.TODO(), deploymentName, v1.GetOptions{})
+	labels := deployment.Spec.Template.ObjectMeta.Labels
+	return len(labels) == 1 && labels[changingLabelKey] != ""
+}

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"flag"
+	"fmt"
 	"os"
 
 	"k8s.io/client-go/kubernetes"
@@ -48,6 +49,17 @@ func main() {
 		os.Exit(1)
 	}
 
+	onlyOneLabel := isTheEditedLabelTheOnlyOne(
+		namespace,
+		clientset,
+		deploymentName,
+		labelToChangeKey,
+	)
+	if onlyOneLabel {
+		logError(fmt.Sprintf("The label \"%s\" can not be edited because it's the only one in the matching set.", labelToChangeKey))
+		os.Exit(1)
+	}
+
 	displaySummary(
 		namespace,
 		deploymentName,