// 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.Update(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
// updateWithRetries updates applies the given rc as an update.
func updateWithRetries(rcClient client.ReplicationControllerInterface, rc *api.ReplicationController, applyUpdate updateFunc) (*api.ReplicationController, error) {
	var err error
	oldRc := rc
	err = wait.Poll(10*time.Millisecond, 1*time.Minute, func() (bool, error) {
		// Apply the update, then attempt to push it to the apiserver.
		if rc, err = rcClient.Update(rc); err == nil {
			// rc contains the latest controller post update
			return true, nil
		// Update the controller with the latest resource version, if the update failed we
		// can't trust rc so use oldRc.Name.
		if rc, err = rcClient.Get(oldRc.Name); err != nil {
			// The Get failed: Value in rc cannot be trusted.
			rc = oldRc
		// The Get passed: rc contains the latest controller, expect a poll for the update.
		return false, nil
	// If the error is non-nil the returned controller cannot be trusted, if it is nil, the returned
	// controller contains the applied update.
	return rc, err