今天早上醒来，我收到 uptimerobot 发来的通知，说某个网站瘫痪了。我自己检查了一下，结果并没有瘫痪。
我通过 ssh 登录并检查了服务器日志，虽然正常请求都可以正常处理，但是 uptimerobot 的请求却是这样的：
1.2.3.4 - - [23/Oct/2015:06:41:06 +0000] "GET / HTTP/1.1" 499 0 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
1.2.3.4 - - [23/Oct/2015:06:41:36 +0000] "GET / HTTP/1.1" 301 5 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
1.2.3.4 - - [23/Oct/2015:06:42:06 +0000] "GET / HTTP/1.1" 499 0 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
1.2.3.4 - - [23/Oct/2015:06:42:36 +0000] "GET / HTTP/1.1" 301 5 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
1.2.3.4 - - [23/Oct/2015:06:43:07 +0000] "GET / HTTP/1.1" 499 0 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
499 是一个 nginx 响应：
301 是从 https 到 http 的重定向，uptimerobot 无法记住（我现在已经更新了 uptimerobot 的设置，但问题仍然存在）。作为参考，以下是一小时前的日志：
1.2.3.4 - - [23/Oct/2015:05:43:07 +0000] "HEAD / HTTP/1.1" 301 0 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
1.2.3.4 - - [23/Oct/2015:05:43:09 +0000] "GET / HTTP/1.1" 200 20564 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
1.2.3.4 - - [23/Oct/2015:05:48:07 +0000] "HEAD / HTTP/1.1" 301 0 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
1.2.3.4 - - [23/Oct/2015:05:48:09 +0000] "GET / HTTP/1.1" 200 20564 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
1.2.3.4 - - [23/Oct/2015:05:53:07 +0000] "HEAD / HTTP/1.1" 301 0 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
1.2.3.4 - - [23/Oct/2015:05:53:09 +0000] "GET / HTTP/1.1" 200 20564 "-" "Mozilla/5.0+(compatible; UptimeRobot/2.0; http://www.uptimerobot.com/)"
这段时间内没有人触碰过服务器。请求（返回 499）被路由到底层服务器（django），一切正常。
这是我的服务器出了问题，还是 uptimerobot 的问题？我监控的其他网站都没有发生这种情况，这些网站有相同的设置。