code: private static ChannelType getChannelType(PropertyKey key, AlluxioConfiguration conf) {
      if (!isNettyEpollAvailable()) {
        return ChannelType.NIO;
      }
      return conf.getEnum(key, ChannelType.class);
    }
docs: Get the proper channel type. Always returns {@link ChannelType} NIO if EPOLL is not available.
  
  @param key the property key for looking up the configured channel type
  @return the channel type to use