Apache event mpm hangs sporadicly

apache-2.4

I'm running apache Apache/2.4.23 (Ubuntu) using event mpm with php-fpm and occasionally apache will just hang for a few minutes. I will get a notification that the server is down and I will investigate and I don't see anything wrong. Error and Access logs don't show anything out of the norm. Server load is low, plenty of memory left, and if I run apachectl status on the cmd line to see the scorecard that will hang. Eventually it will load after a few minutes with the entire scorecard set to W, and the site will start loading again. This happens about once a day with a new server setup and I have a feeling its something to do with my mpm event configuration. Does anyone know what could be causing this?

Best Answer

We have been debugging an issue today, that fits your description perfectly. We experienced this issue on Apache 2.4.25 on Debian Stretch.

From reading GDB thread dumps and Googling for suspicious looking symbols, we eventually found this bug report, that seemed to fit the problem:

https://bz.apache.org/bugzilla/show_bug.cgi?id=60956

It seems that the bug was introduced in Apache 2.4.12, and finally fixed in 2.4.28. We backported Apache 2.4.33 from Debian Buster to Stretch. We'll have to monitor the server for a few days to be sure, but we're quite confident that this has fixed it for us.

Related Solutions

Httpd – Apache MPM event in Apache 2.4+

The prefork MPM has not been the "preferred" MPM for many years.

The reason it is still the default for many distros is that some third-party libraries have trouble with the threading in the worker MPM (which has been the preferred MPM since version 2.2).

Not modules like mod_php, which is quite thread-safe, but libraries used by modules like mod_php, such as mysqli etc.

In 2.4, we have now switched to the STABLE event MPM.

The release is still very new and the documentation has not been completely updated to reflect this.

As has been the case for years, if the prefork MPM is causing you grief, switch to threaded serving and run your dynamic content via fastCGI.

Switching from MPM Worker to Event with PHP-FPM

Found that I needed to make the final lines of my php.conf conditional.

<IfModule mpm_prefork_module>
#
# Apache specific PHP configuration options
# those can be override in each configured vhost
#
php_value session.save_handler "files"
php_value session.save_path "/var/lib/php/session"
</IfModule>

Best Answer

Related Solutions

Httpd – Apache MPM event in Apache 2.4+

Switching from MPM Worker to Event with PHP-FPM

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