@Subscribe
  @AllowConcurrentEvents
  public void onAmbariEvent(AlertDefinitionRegistrationEvent event) {
    LOG.debug("Received event {}", event);

    AlertDefinition definition = event.getDefinition();

    LOG.debug("Registering alert definition {}", definition);

    if (definition.getSource().getType() == SourceType.AGGREGATE) {
      m_aggregateMapping.registerAggregate(event.getClusterId(), definition);
    }
  }
Handles {@link AlertDefinitionRegistrationEvent} by performing the
following tasks:
<ul>
<li>Registration with {@link AggregateDefinitionMapping}</li>
</ul>

@param event
         the event being handled.
ambari-server/src/main/java/org/apache/ambari/server/events/listeners/alerts/AlertLifecycleListener.java