[apacheignite]Adding user-defined behavior to the Ignite Coordinator?

Question

Is there a way to add a specific behavior that should only be executed on (and follow) the Ignite Coordinator ServerNode?

Is there a add-on hook to add some customer specific behavior?

Thanks in advance.

Greg

Answer 1

AFAIK, there is not any built-in hook to achieve this. However, it can be achieved through Node Singleton Ignite Service and using an api on TcpDiscoverySpi.isLocalNodeCoordinator().

If different discovery mechanism other than TcpDiscovery, is used, above mentioned way by @Alexandr can be used to get a co-ordinator node.

1. Define an Ignite Service as follows. It will schedule a task that will periodically execute on every node of the cluster and execute certain logic, if it's a coordinator node.

   public class IgniteServiceImpl implements Service {

    @IgniteInstanceResource
    Ignite ignite;
   
    @Override
    public void cancel(ServiceContext ctx) {
    }
   
    @Override
    public void init(ServiceContext ctx) throws Exception {
        System.out.println("Starting a service");
    }
   
    @Override
    public void execute(ServiceContext ctx) throws Exception {
   
        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                System.out.println("Inside a service");
                if (ignite != null) {
                    DiscoverySpi discoverySpi = ignite.configuration().getDiscoverySpi();
                    if (discoverySpi instanceof TcpDiscoverySpi) {
                        TcpDiscoverySpi tcpDiscoverySpi = (TcpDiscoverySpi) discoverySpi;
                        if(tcpDiscoverySpi.isLocalNodeCoordinator())
                            doSomething();
                    } else {
                        ClusterNode coordinatorNode = ((IgniteEx) ignite).context().discovery().discoCache().oldestAliveServerNode();
                        UUID localNodeId = ((IgniteEx) ignite).context().localNodeId();
                        if(localNodeId.equals(coordinatorNode.id()))
                            doSomething();
                    }
                } else {
                    System.out.println("Ignite is null");
                }
            }
        }, 5, (30 * 1000L));
    }
   
    private void doSomething(){
        System.out.println("Hi I am Co-ordinator Node");
    }
   

   }

2. Start above service as node singleton using Ignite.services() as follows

    IgniteConfiguration igniteConfiguration = new IgniteConfiguration();
    igniteConfiguration.setIgniteInstanceName("ignite-node");
    Ignite ignite = Ignition.start(igniteConfiguration);
   
    IgniteServices services = ignite.services();
    services.deployNodeSingleton("test-service",new IgniteServiceImpl());
   

Answer 2

In case of a low-level logic, you can extend Ignite with custom plugins. I'm not sure if there is an easy way to check if a node is indeed the coordinator, but you might check for the oldest one:

private boolean isCoordinator() {
        ClusterNode node = ((IgniteEx)ignite()).context().discovery().discoCache().oldestAliveServerNode();

        return node != null && node.isLocal();
    }

Otherwise, just run a custom initialization logic/compute task, once a node is started.