Add a warning when FPM is used with MPM_PREFORK

[nickvergessen]

Fix #7499

[danxuliu]

Funny fact, apachectl -M can fail when executed through the web server even if it works when executed as root if any of the modules needs to read a file accessible only by root (for example, the SSH certificates). Of course that is a corner case, but I wonder if that could fail too in more common scenarios.

Independently of that, what about SystemKeeper's suggestion to rely on the .htaccess file? That would require mod_env to be set, but that is needed anyway for the default setup of Nextcloud (SetEnv is used in the main .htaccess file and if the variable is not found an error is shown in the setup checks).

And for reference, I was able to reproduce the performance problem when using FPM and mpm_prefork if several clients were long polling.

[nickvergessen]

The problem is this would need to go into the root .htaccess file of Nextcloud as that is where index.php is what serves the settings page?

[danxuliu]

The problem is this would need to go into the root .htaccess file of Nextcloud as that is where index.php is what serves the settings page?

Mmm, right, htaccess files do not seem to have effect for PHP files in subdirectories if they are loaded by other PHP files rather than directly by the web server :-(

[danxuliu]

Not a fan of calling apachectl, but apparently that approach is the only one that (except on corner cases) works 🤷, so 👍

But, what happens if NGINX is used instead?

[nickvergessen]

It bails out with being a "valid configuration"
So we are not showing the error.

[nickvergessen]

Failing test is fixed by #7517

So merging

[prismopensource]

Test still fails when running Nextcloud on a semi popular web control panel I'm afraid, when I check on a standard Apache with PHP 8.2 in php-fpm mode:

# httpd -V | grep 'MPM'
Server MPM:     event

Though I'm still getting a "It seems that the PHP and Apache configuration is not compatible. Please note that PHP can only be used with the MPM_PREFORK module and PHP-FPM can only be used with the MPM_EVENT module." warning.