@Subscribe
  public void onMetricsCollectorHostDownEvent(MetricsCollectorHostDownEvent event) {

    LOG.debug("MetricsCollectorHostDownEvent caught, Down collector : {}", event.getCollectorHost());

    String clusterName = event.getClusterName();
    if (externalMetricCollectorsState.containsKey(clusterName)) {
      if (externalCollectorDownRefreshCounter.testRefreshCounter()) {
        externalMetricCollectorsState.get(clusterName).put(event.getCollectorHost(), false);
      }
    } else {
      MetricsCollectorHAClusterState collectorHAClusterState = clusterCollectorHAState.get(clusterName);
      collectorHAClusterState.onCollectorHostDown(event.getCollectorHost());
    }
  }
Handles {@link MetricsCollectorHostDownEvent}

@param event the change event.
ambari-server/src/main/java/org/apache/ambari/server/controller/metrics/MetricsCollectorHAManager.java