code: @Override
      @Synchronized
      public void registerHost(Host host) {
          Preconditions.checkNotNull(host, "host");
          Exceptions.checkArgument(!entryMap.containsKey(host), "host", "host is already registered to cluster.");
  
          String hostPath = ZKPaths.makePath(getPathPrefix(), host.toString());
          PersistentNode node = new PersistentNode(client, CreateMode.EPHEMERAL, false, hostPath,
                  host.toBytes());
  
          node.start(); //start creation of ephemeral node in background.
          entryMap.put(host, node);
      }
docs: Register Host to cluster.
  
  @param host Host to be part of cluster.