code: void setLastSeenConfig(ClusterConfiguration conf) throws IOException {
      String version = conf.getVersion().toSimpleString();
      File file = new File(rootDir, String.format("cluster_config.%s", version));
      FileUtils.writePropertiesToFile(conf.toProperties(), file);
      // Since the new config file gets created, we need to fsync the directory.
      fsyncDirectory();
    }
docs: Updates the last seen configuration.
  
  @param conf the updated configuration.
  @throws IOException in case of IO failure.