code: func (rsc *ReplicaSetController) enqueueReplicaSetAfter(obj interface{}, after time.Duration) {
  	key, err := controller.KeyFunc(obj)
  	if err != nil {
  		utilruntime.HandleError(fmt.Errorf("couldn't get key for object %+v: %v", obj, err))
  		return
  	}
  	rsc.queue.AddAfter(key, after)
  }
docs: // obj could be an *apps.ReplicaSet, or a DeletionFinalStateUnknown marker item.