@VisibleForTesting
  void consumeInitialInstances(LlapRegistryService service) throws IOException {
    LlapServiceInstanceSet serviceInstances = service.getInstances();
    for (LlapServiceInstance serviceInstance :
            serviceInstances.getAll()) {
      onCreate(serviceInstance, -1);
    }
  }
Collect metrics from the llap daemons in every given milliseconds.
llap-tez/src/java/org/apache/hadoop/hive/llap/tezplugins/metrics/LlapMetricsCollector.java