delay start of controller until resource is found

[jvrahav]

Is there a way to delay start of a controller until a resource exists in the apiserver.

Say i want to watch resource types A and B. However i want to do this only after some other process has created a resource of resource type C

I need this to avoid watching for resources until a dependent resource exists in the system, resource of type C. This way i can ensure my controller is not consuming resources unless it is required.

Thanks,
Rahav

[whg517]

I think you can customize the coordinator's SetupWithManager method to trigger the resources that need to be coordinated while listening for the required resource changes.

example code :

// SetupWithManager sets up the controller with the Manager.
func (r *ListenerReconciler) SetupWithManager(mgr ctrl.Manager) error {
	return ctrl.NewControllerManagedBy(mgr).
		For(&listeners.Listener{}).
		Watches(&corev1.Endpoints{}, handler.TypedEnqueueRequestsFromMapFunc(r.handleEndpointsChanges)).
		Watches(&corev1.PersistentVolume{}, handler.EnqueueRequestsFromMapFunc(r.handlePVChanges)).
		Watches(&listeners.ListenerClass{}, handler.EnqueueRequestsFromMapFunc(r.handleListenerClassChanges)).
		Complete(r)
}

func (r *ListenerReconciler) handleListenerClassChanges(ctx context.Context, obj client.Object) []ctrl.Request {
	listenerClass := obj.(*listeners.ListenerClass)
	list := &listeners.ListenerList{}
	if err := r.List(ctx, list); err != nil {
		return nil
	}

	requests := make([]ctrl.Request, 0)
	for _, listener := range list.Items {
		if listener.Spec.ClassName == listenerClass.Name {
			requests = append(requests, reconcile.Request{
				NamespacedName: client.ObjectKey{
					Name:      listener.Name,
					Namespace: listener.Namespace,
				},
			})
		}
	}

	return requests
}

func (r *ListenerReconciler) handleEndpointsChanges(ctx context.Context, obj client.Object) []ctrl.Request {
	endpoints := obj.(*corev1.Endpoints)
	list := &listeners.ListenerList{}
	if err := r.List(ctx, list); err != nil {
		return nil
	}

	requests := make([]ctrl.Request, 0)
	for _, listener := range list.Items {
		if listener.Status.ServiceName == endpoints.Name {
			requests = append(requests, reconcile.Request{
				NamespacedName: client.ObjectKey{
					Name:      listener.Name,
					Namespace: listener.Namespace,
				},
			})
		}
	}

	return requests
}