<?php

if ($db_link = mysqli_connect('localhost', 'nagios', '', '')) {

  mysqli_close($db_link);
  /* 200 OK */
  http_response_code(200);
  echo "200 OK\n";

} else {

  /* 503 Service Unavailable */
  http_response_code(503);
  echo "503 Service Unavailable\n";

}