Cloudflare returns 522 timeout errors when trying to connect to Apache PHP-FPM

I have a CWP Pro virtual server running AlmaLinux 8.10 and CWP 1.14

The server is never under any appreciable load - max 33% of processor capacity and 4GB of RAM from 16GB total. Checking the Apache Server Status via the CWP control panel, everything looks sane - 12 spawned servers, utilises 1.5GB RAM, 272 tasks.

All sites on the server use PHP-FPM, some stuck on legacy PHP7.4 but most running PHP8.3

Cloudflare returns a timeout error of 522 on some sites, seemingly at random but rather often. If I disable Cloudflare, I get the same timeouts but with a vanilla error message in the browser. So Cloudflare is not at fault here.

I have tried various tactics to prevent this:

a) Apache was reporting it had run out of RequestWorker processes, so I included the following snippet via conf/extra/httpd-mpm.conf (Apache runs with the MPM Evnt mod on my server).

Code: [Select]

<IfModule mpm_event_module>
    StartServers            25
    ServerLimit             32
    MinSpareThreads         75
    MaxSpareThreads        250
    ThreadsPerChild         25
    MaxRequestWorkers    800
    MaxConnectionsPerChild   0
</IfModule>

b) When that didn't solve the problem, I also increased the number of max PHP-FPM processes in the default template and for individual sites. I increased from the default of MaxChildProcceses 4 to 25.

c) I enabled KeepAlive which I don't think is enabled by default, via self-authored snippet included in conf/extra/httpd-keepalive.conf

Code: [Select]

KeepAlive On
MaxKeepAliveRequests 100
KeepAliveTimeout 5

None of the above has resolved the problem. I am at a loss. Furthermore, some of the sites show extremely poor performance. Yet the server has loads of spare capacity.

Anyone got any insight here?

I have checked if disabling the firewall made any difference (in case it was blocking Cloudflare IP addresses). It did not and it is not.