我们在aws中有一个自动缩放组，启动时数据库连接超时。这是一个zend framework 1应用程序，在ubuntu 16.04.3 lts上使用PHP7.0.22-0ubuntu0.16.04.1
代码被烘焙到ami中，但在启动过程中，userdata脚本将从git中提取并配置应用程序。数据库域多年来没有改变，配置主要是考虑使用哪个elasticache示例。换句话说，baked-in代码已经配置了数据库，并且在configure步骤中被相同的值覆盖。
一旦ec2示例在elb中，它就开始受到攻击 /health-check 查看负载平衡器是否正常。此控制器内有以下代码：

public function healthCheckAction() {
  try {
    /* @var $DBConn Zend_Db_Adapter_Pdo_Mysql */
    $DBConn = Zend_Registry::get('multidb')->getDb();

    // test guide service (most likely will be from memcache, unlikely to hit db)
    $guideService = $this->_apiGuideService();
    $guideService->isLoaded();

    // this line fails and throws an exception
    // I put host in here just so an error would include it in throw during this phase instead of catch phase (where it works)
    // test raw db connection
    $dbh = new PDO("mysql:host={$DBConn->getConfig()['host']};dbname={$DBConn->getConfig()['dbname']}", $DBConn->getConfig()['username'], $DBConn->getConfig()['password']);
    $data = $dbh->query("SELECT '{$DBConn->getConfig()['host']}' as host, now()")->fetchObject();

    // test database connectivity
    // I put host in here just so an error would include it in throw during this phase instead of catch phase (where it works)
    $sql = "SELECT '{$DBConn->getConfig()['host']}' as host, now()";
    $DBConn->fetchRow($sql);

    // test cache
    /* @var $cache Zend_Cache_Core */
    $cache = Zend_Registry::get('cachemanager')->getCache('default');
    if (!$cache->load('health_check')) {
      $cache->save(true, 'health_check');
    }

    echo 'Instance is healthy';
  }
  catch (Exception $e) {
    header('HTTP/1.1 500 Internal Server Error');
    echo 'Instance is unhealthy';

    // get instance id
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, 'http://169.254.169.254/latest/meta-data/public-ipv4');
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

    // get instance ip
    $ip = curl_exec($ch);
    curl_setopt($ch, CURLOPT_URL, 'http://169.254.169.254/latest/meta-data/instance-id');
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    $instance = curl_exec($ch);

    // email us some info
    $message = "Instance $instance failed health check.  ssh ubuntu@$ip to investigate<br><br>" . $e->getLine() . " " . $e->getCode() . "<br>" . $e->getMessage() . "<br>" . $e->getTraceAsString(). "<br><br>";
    ob_start();

    // this works and returns access denied, not timeout
    $this->runCommand('mysql -u examplecom_platform -h sg-rds-example.us-east-1.rds.amazonaws.com');

    echo "testing DB with php<br>";
    try {
      echo "write host: " . $DBConn->getConfig()['host'] . "<br>";
      echo "read host: " . $DBConn->getConfig()['host'] . "<br>";
      $dbh = new PDO("mysql:host={$DBConn->getConfig()['host']};dbname={$DBConn->getConfig()['dbname']}", $DBConn->getConfig()['username'], $DBConn->getConfig()['password']);
      $data = $dbh->query('select now()')->fetchObject();
      echo "query database without zend:<br>";
      print_r($data);
      // this line works and prints out
      //  stdClass Object
      //  (
      //  [now()] => 2018-01-09 14:47:12
      //  )

      $dbh = null;
    } catch (PDOException $e) {
      print "Error: " . $e->getMessage() . "<br/>";
    }

    // this all work/show correct IP
    $this->runCommand('nc -vz sg-rds-example.us-east-1.rds.amazonaws.com 3306');
    $this->runCommand('host sg-rds-example.us-east-1.rds.amazonaws.com');
    $this->runCommand('dig sg-rds-example.us-east-1.rds.amazonaws.com');
    $debug = ob_get_contents();
    ob_end_clean();
    $message .= "<br><br>" . str_replace("\n", "<br>", $debug);

    $mail = new Zend_Mail();
    $mail->setSubject('[examplecom] Instance Failed Healthcheck v2')
      ->setFrom('noreply@example.com')
      ->addTo('alerts@example.com')
      ->setBodyHtml($message)
      ->send();
  }
}

当我不断调试东西时，我会添加越来越多的东西来测试连接
这个 try 语句抛出错误 SQLSTATE[HY000] [2002] Connection timed out 但这种完全相同的联系在 catch 并且能够查询 now() 从数据库。
这就是我被难住的地方，同一个进程在第一次连接时超时，但在错误捕捉过程中却能工作？
另外，我只会收到1或2的这些电子邮件说，它不能连接，但最终的时候，我可以登录测试一些东西，它是工作和连接良好。健康检查报告快乐，示例保存在elb中。
有什么想法或建议添加更多的调试？