public function checkUrl($url) {
    try {
      $client = new Client();
      $res = $client->request('GET', $url, [
        'connection_timeout' => 2,
        'timeout' => 2,
        'exceptions' => FALSE,
      ]);
      if ($res->getStatusCode() && substr($res->getStatusCode(), 0, 1) != '5') {
        return TRUE;
      }
      else {
        $this->logger->debug($res->getBody());
        return FALSE;
      }
    }
    catch (\Exception $e) {
      $this->logger->debug($e->getMessage());
    }
    return FALSE;
  }