code: func (a *Location) Distance(b *Location) float64 {
  	if a.DataCenter != b.DataCenter {
  		return 1000
  	}
  	if a.Rack != b.Rack {
  		return 100
  	}
  	if a.Server != b.Server {
  		return 10
  	}
  	return 1
  }
docs: // the distance is a relative value, similar to network lantency