// updateReplicaCount attempts to update the Status.Replicas of the given controller, with a single GET/PUT retry.
func updateReplicaCount(rcClient client.ReplicationControllerInterface, controller api.ReplicationController, numReplicas int) (updateErr error) {
	// This is the steady state. It happens when the rc doesn't have any expectations, since
	// we do a periodic relist every 30s. If the generations differ but the replicas are
	// the same, a caller might've resized to the same replica count.
	if controller.Status.Replicas == numReplicas &&
		controller.Generation == controller.Status.ObservedGeneration {
		return nil
	}
	// Save the generation number we acted on, otherwise we might wrongfully indicate
	// that we've seen a spec update when we retry.
	// TODO: This can clobber an update if we allow multiple agents to write to the
	// same status.
	generation := controller.Generation

	var getErr error
	for i, rc := 0, &controller; ; i++ {
		glog.V(4).Infof("Updating replica count for rc: %v, %d->%d (need %d), sequence No: %v->%v",
			controller.Name, controller.Status.Replicas, numReplicas, controller.Spec.Replicas, controller.Status.ObservedGeneration, generation)

		rc.Status = api.ReplicationControllerStatus{Replicas: numReplicas, ObservedGeneration: generation}
		_, updateErr = rcClient.UpdateStatus(rc)
		if updateErr == nil || i >= statusUpdateRetries {
			return updateErr
		}
		// Update the controller with the latest resource version for the next poll
		if rc, getErr = rcClient.Get(controller.Name); getErr != nil {
			// If the GET fails we can't trust status.Replicas anymore. This error
			// is bound to be more interesting than the update failure.
			return getErr
		}
	}
}