code: public void locateCluster(String cluster, Handler<AsyncResult<String>> doneHandler) {
      Set<String> registry = vertx.sharedData().getSet(cluster);
      synchronized (registry) {
        if (!registry.isEmpty()) {
          locateNode(cluster, new HashSet<>(registry), doneHandler);
        }
      }
    }
docs: Locates the local address of the nearest node if one exists.
  
  @param cluster The cluster in which to search for the node.
  @param doneHandler A handler to be called once the address has been located.