docs: def on_discovery_add(self, discovery):
          """
          When a discovery is added we call `connect()` on it and launch a thread
          for each cluster where the discovery watches for changes to the
          cluster's nodes.
          """
          discovery.connect()
  
          for cluster in self.configurables[Cluster].values():
              if cluster.discovery != discovery.name:
                  continue
  
              self.launch_thread(
                  cluster.name, discovery.start_watching,
                  cluster, self.sync_balancer_files
              )
  
          self.sync_balancer_files()