Error 521 - Nothing useful in Apache or Mysql log

I am running Wordpress on Apache server with Ubuntu 18 LTS

I have received an intermittent Error 521 on my website this morning when previewing a post. Following this the whole site was down (521 host down).

I checked my Apache2 error log and the only thing in the log is this, from several hours before:

[Tue Jul 09 06:25:40.040855 2019] [mpm_prefork:notice] [pid 995] AH00163: Apache/2.4.29 (Ubuntu) OpenSSL/1.1.0g configured – resuming normal operations
[Tue Jul 09 06:25:40.040884 2019] [core:notice] [pid 995] AH00094: Command line: ‘/usr/sbin/apache2’

There is also nothing in the MySQL error log problem related.
Is there anywhere else I can check that could explain why the site went down? I rebooted and it is back up now.

Swap: around 200MB out of 1GB pool
CPU was fine, no more than 20%
Memory also fine probably around 60% including cache / buffers

That sure sounds like some sort of rate limiting. It could be happening upstream from Apache. But it only happens on previews? Have you asked your host?

1 Like

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.