code: ClusterConfiguration getLastSeenConfig() throws IOException {
      File file = getLatestFileWithPrefix(this.rootDir, "cluster_config");
      if (file == null) {
        return null;
      }
      try {
        Properties prop = FileUtils.readPropertiesFromFile(file);
        return ClusterConfiguration.fromProperties(prop);
      } catch (FileNotFoundException e) {
        LOG.debug("AckConfig file doesn't exist, probably it's the first time" +
            "bootup.");
      }
      return null;
    }
docs: Gets last seen configuration.
  
  @return the last seen configuration.
  @throws IOException in case of IO failure.