I had a real battle getting HTTP/2 to work on my new AMI2 Lamp webserver this week. The Apache http2 module was installed but it didn't work alongside mod_mpm_prefork, so I needed to switch to the mod_mpm_event module. However this wouldn't start unless the server was using php-fpm. So what seemed like a simple task of just upgrading my HTTP requests to HTTP/2, turned into a little bit of work and searching on Google didn't offer much assistance as everyone else seemed to be using a Debian based linux which had a2enmod available.
The article is really just in note form for my own reference, but I hope it points you in the right direction if you're having problems getting it all to work.
php-fpm:
Make sure php-fpm is installed. PHP FPM is an article in it's own right, but the following might be useful:
> sudo yum install -y php-fpm
Once it's installed, make sure php-fpm is running as a service:
> sudo systemctl start php-fpm
Make sure it starts on reboot.
> sudo systemctl enable php-fpm
Make sure it's listening on 127.0.0.1:9000
> sudo vi /etc/php-fpm.d/www.conf
Edit the config file above (assuming that's where it is on your computer) and change the following:
;listen = /run/php-fpm/www.sock
You can confirm if Apache is processing requests using PHP-FPM via the phpinfo() output.
Apache:
Make sure Apache is configured to use event MPM.
> sudo vi /etc/httpd/conf.modules.d/00-mpm.conf#LoadModule mpm_prefork_module modules/mod_mpm_prefork.so
Make sure PHP is processing with php-fpm
ProxyPassMatch ^/(.*\.php(/.*)?)$ fcgi://127.0.0.1:9000/var/www/html/$1DirectoryIndex /index.php index.php#<FilesMatch \.(php|phar)$>
UPDATE 19/5/2023: Alternatively you can leave it as listen = /run/php-fpm/www.sock in /etc/php-fpm.d/www.conf but if that's the case omit adding ProxyPassMatch ^/(.*\.php(/.*)?)$ fcgi://127.0.0.1:9000/var/www/html/$1 to /etc/httpd/conf.d/php.conf as well.
Important bit:
Make sure mod_php is not installed.
This was the important one for me. The error message I was getting before doing the above was 'Apache is running a threaded MPM, but your PHP Module is not compiled to be threadsafe.'.
HTTP/2:
> sudo vi /etc/httpd/conf.d/ssl.conf# enable HTTP/2, if available
Useful commands:
> sudo service php-fpm reload
Useful resources:
https://wiki.alpinelinux.org/wiki/Apache_with_php-fpm
https://donjajo.com/fix-apache-running-threaded-mpm-php-module-not-compiled-threadsafe-fedora/
https://cwiki.apache.org/confluence/display/HTTPD/PHP-FPM
https://computingforgeeks.com/install-apache-with-ssl-http2-on-rhel-centos/
https://stackoverflow.com/questions/71875777/enable-http2-in-apache-2-4-53
https://httpd.apache.org/docs/2.4/mod/mod_http2.html