If it possible to connect from ApplicationManager to MetaScheduler via XML RPC

[xni]

Yes. This is a fake Python3 metascheduler:

from xmlrpc.server import SimpleXMLRPCServer
from xmlrpc.server import SimpleXMLRPCRequestHandler

# Restrict to a particular path.
class RequestHandler(SimpleXMLRPCRequestHandler):
    rpc_paths = ('/xmlrpc',)

# Create server
server = SimpleXMLRPCServer(("0.0.0.0", 9000),
                            requestHandler=RequestHandler)
server.register_introspection_functions()

def get_task():
    return 42

server.register_function(get_task, 'GetTask')
server.serve_forever()

Then I put some xmlrps JARs to default CLASSPATH on ApplicationMaster machine (in furcher we should find a way to distribute them. May be via HDFS). And changed a ApplicationMasters code:

public void run() throws YarnException, IOException {
    amRMClient = AMRMClientAsync.createAMRMClientAsync(1000, new RMCallbackHandler());
    amRMClient.init(conf);
    amRMClient.start();

    RegisterApplicationMasterResponse response;
    response = amRMClient.registerApplicationMaster(NetUtils.getHostname(), -1, "");
    LOG.info("ApplicationMaster is registered with response: {}", response.toString());

    // As a client!
    YarnConfiguration conf = new YarnConfiguration();
    YarnClient yarnClient = YarnClient.createYarnClient();
    yarnClient.init(conf);
    yarnClient.start();

    List<NodeReport> nodeReports = yarnClient.getNodeReports();
    int total_memory = 0;
    for (NodeReport report :nodeReports) {
        total_memory += report.getUsed().getMemory();
    }
    if (total_memory > 1000) {
        // Get Task
        XmlRpcClientConfigImpl metaSchedulerConfig = new XmlRpcClientConfigImpl();
        metaSchedulerConfig.setServerURL(new URL("http://192.168.7.1:9000/xmlrpc"));
        XmlRpcClient client = new XmlRpcClient();
        client.setConfig(metaSchedulerConfig);
        try {
            Integer result = (Integer) client.execute("GetTask", new Object[]{});
            LOG.info("Got task: " + result.toString());
        } catch (XmlRpcException e) {
            e.printStackTrace();
        }
    }
    yarnClient.stop();
    LOG.info("Containers have all completed, so shutting down NMClient and AMRMClient...");

    nmClient.stop();
    amRMClient.unregisterApplicationMaster(FinalApplicationStatus.SUCCEEDED, "Application complete!", null);
    amRMClient.stop();
}

Output:

14/07/27 19:37:14 INFO yarntest.ApplicationMaster: Got task: 42