public HelixAggregatedViewClusterInfo start() throws Exception {
    try {
      HelixAggregatedViewClusterInfo clusterInfo = initialize();
      if (exception != null) {
        // We could have hit an error in one of the helix listener callbacks in HelixClusterChangeHandler. In such cases,
        // rethrow the exception.
        throw exception;
      } else {
        return clusterInfo;
      }
    } catch (Exception e) {
      logger.warn("Exception while initializing cluster", e);
      throw e;
    }
  }
Begin the startup procedure for connecting (and registering listeners) for getting cluster information from helix
service.
@return {@link HelixAggregatedViewClusterInfo} containing the information associated with view cluster.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/HelixAggregatedViewClusterInitializer.java