private DataNodeConfig getDataNodeConfig() {
    DataNodeConfig dataNodeConfig = dataNodeConfigSource.get(instanceName);
    if (dataNodeConfig == null) {
      throw new IllegalStateException(
          "No config found for cluster: \"" + clusterName + "\", instance: \"" + instanceName + "\"");
    }
    return dataNodeConfig;
  }
@return {@link DataNodeConfig} of current participant (The method also checks the existence of the config).
ambry-clustermap/src/main/java/com/github/ambry/clustermap/HelixParticipant.java