/**
   * Change topology.
   *
   * @param parent Grid to execute tasks on.
   * @param add New nodes count.
   * @param rmv Remove nodes count.
   * @param type Type of nodes to manipulate.
   */
  private static void changeTopology(Ignite parent, int add, int rmv, String type) {
    Collection<ComputeTaskFuture<?>> tasks = new ArrayList<>();

    IgniteCompute comp = parent.compute().withAsync();

    // Start nodes in parallel.
    while (add-- > 0) {
      comp.execute(ClientStartNodeTask.class, type);

      tasks.add(comp.future());
    }

    for (ComputeTaskFuture<?> task : tasks) task.get();

    // Stop nodes in sequence.
    while (rmv-- > 0) parent.compute().execute(ClientStopNodeTask.class, type);

    // Wait for node stops.
    // U.sleep(1000);

    Collection<String> gridNames = new ArrayList<>();

    for (Ignite g : G.allGrids()) gridNames.add(g.name());

    parent.log().info(">>> Available grids: " + gridNames);
  }
  /**
   * Example for start/stop node tasks.
   *
   * @param args Not used.
   */
  public static void main(String[] args) {
    String nodeType = "tcp+ssl";

    // Start initial node = 1
    try (Ignite g = G.start(NODE_CFG.get(nodeType))) {
      // Change topology.
      changeTopology(g, 4, 1, nodeType);
      changeTopology(g, 1, 4, nodeType);

      // Stop node by id = 0
      g.compute().execute(ClientStopNodeTask.class, g.cluster().localNode().id().toString());

      // Wait for node stops.
      // U.sleep(1000);

      assert G.allGrids().isEmpty();
    } catch (Exception e) {
      System.err.println("Uncaught exception: " + e.getMessage());

      e.printStackTrace(System.err);
    }
  }