code: func (s *PresenceService) GetReverseTunnels(opts ...services.MarshalOption) ([]services.ReverseTunnel, error) {
  	startKey := backend.Key(reverseTunnelsPrefix)
  	result, err := s.GetRange(context.TODO(), startKey, backend.RangeEnd(startKey), backend.NoLimit)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	tunnels := make([]services.ReverseTunnel, len(result.Items))
  	for i, item := range result.Items {
  		tunnel, err := services.GetReverseTunnelMarshaler().UnmarshalReverseTunnel(
  			item.Value, services.AddOptions(opts, services.WithResourceID(item.ID), services.WithExpires(item.Expires))...)
  		if err != nil {
  			return nil, trace.Wrap(err)
  		}
  		tunnels[i] = tunnel
  	}
  	// sorting helps with tests and makes it all deterministic
  	sort.Sort(services.SortedReverseTunnels(tunnels))
  	return tunnels, nil
  }
docs: // GetReverseTunnels returns a list of registered servers