Fix the issue of unable to complete scaling down from 1 to 0.

pkg/externalscaler/externalscaler.go

@@ -16,10 +16,24 @@ type ExternalScaler struct {
 func (e *ExternalScaler) mustEmbedUnimplementedExternalScalerServer() {
 }
 
-func (e *ExternalScaler) IsActive(ctx context.Context, scaledObject *ScaledObjectRef) (*IsActiveResponse, error) {
-	return &IsActiveResponse{
-		Result: true,
-	}, nil
+func (e *ExternalScaler) IsActive(ctx context.Context, scaledObjectRef *ScaledObjectRef) (*IsActiveResponse, error) {
+        name := scaledObjectRef.GetName()
+        ns := scaledObjectRef.GetNamespace()
+        gss := &gamekruiseiov1alpha1.GameServerSet{}
+        err := e.client.Get(ctx, types.NamespacedName{Namespace: ns, Name: name}, gss)
+        if err != nil {
+                klog.Error(err)
+                return nil, err
+        }
+        currentReplicas := gss.Status.CurrentReplicas
+        numWaitToBeDeleted := gss.Status.WaitToBeDeletedReplicas
+        if numWaitToBeDeleted == nil {
+                return nil, fmt.Errorf("GameServerSet %s/%s has not inited", ns, name)
+        }
+        desireReplicas := currentReplicas - *numWaitToBeDeleted
+        return &IsActiveResponse{
+                Result: desireReplicas > 0,
+        }, nil
 }
 
 func (e *ExternalScaler) StreamIsActive(scaledObject *ScaledObjectRef, epsServer ExternalScaler_StreamIsActiveServer) error {