controller runtime: GrandPa, Son, GrandSon and setting OwnerReferences

I write a Kubernetes controller with controller-runtime.

Imagine there are three CRDs: GrandPa, Son, and GrandSon. Each has its own controller in a separate deployment.

I am writing the GrandPa controller. When the user creates a GrandPa object, my controller creates a Son object and uses SetControllerReference(grandpa, son).

The Son controller detects the new Son object, creates a GrandSon object, and uses SetControllerReference(son, grandson).

My GrandPa controller needs its Reconcile() function to be triggered when a GrandSon object changes.

Afaik .Owns() does not work for GrandPa watching GrandSon because the ownership chain is indirect (GrandPa -> Son -> GrandSon).

I can only change the source code of GrandPa controller.

How to get Reconcile() of GrandPa get triggered when GrandSon changes?

Your question is pretty generic, however from what I can understand, you should use Watches() to make GrandPa reconcile when a GrandSon changes. Since GrandPa isn’t a direct owner, manually map GrandSon to GrandPa through Son, like so:

err = ctrl.NewControllerManagedBy(mgr).
    For(&GrandPa{}).
    Owns(&Son{}).
    Watches(
        &source.Kind{Type: &GrandSon{}},
        handler.EnqueueRequestsFromMapFunc(func(grandson client.Object) []reconcile.Request {
            var sonRef *metav1.OwnerReference
            for _, owner := range grandson.GetOwnerReferences() {
                if owner.Kind == "Son" {
                    sonRef = &owner
                    break
                }
            }
            if sonRef == nil {
                return nil
            }

            son := &Son{}
            if err := mgr.GetClient().Get(context.TODO(), types.NamespacedName{
                Name:      sonRef.Name,
                Namespace: grandson.GetNamespace(),
            }, son); err != nil {
                return nil
            }

            var grandpaRef *metav1.OwnerReference
            for _, owner := range son.GetOwnerReferences() {
                if owner.Kind == "GrandPa" {
                    grandpaRef = &owner
                    break
                }
            }
            if grandpaRef == nil {
                return nil
            }

            return []reconcile.Request{{
                NamespacedName: types.NamespacedName{
                    Name:      grandpaRef.Name,
                    Namespace: son.GetNamespace(),
                },
            }}
        }),
    ).Complete(r)