@Override
  public void close(String connectionId) {
    SelectionKey key = keyForId(connectionId);
    if (key == null) {
      metrics.selectorCloseKeyErrorCount.inc();
      logger.error("Attempt to close socket for which there is no open connection. Connection id {}", connectionId);
    } else {
      close(key);
    }
  }
Begin closing this connection by given connection id
ambry-network/src/main/java/com/github/ambry/network/Selector.java