====== Apache Web Server Tuning ======
Change default Apache ''prefork'' to ''event'' module.

===== For Ubuntu =====
https://www.interserver.net/tips/kb/apache-php-fpm-ubuntu-18-04/
<code>
a2dismod mpm_prefork
a2dismod mpm_worker
a2enmod mpm_event
systemctl restart apache2
</code>

==== With PHP ====
<code>
aptitude install php-fpm libapache2-mod-fcgid
a2enmod proxy
a2enmod proxy_fcgi
a2dismod php7.4
a2enconf php7.4-fpm
a2dismod mpm_prefork
a2dismod mpm_worker
a2enmod mpm_event
systemctl restart apache2
</code>


===== Enable to Event Module =====
  * Edit /etc/httpd/conf.modules.d/00-mpm.conf
  * Comment Line: LoadModule mpm_prefork_module modules/mod_mpm_prefork.so
  * Uncomment Line: LoadModule mpm_event_module modules/mod_mpm_event.so

===== Include Configuration File for MPM Event Module =====
  * In /etc/httpd/conf/httpd.conf
  * Add Line: IncludeOptional conf.d/mpm_event_module.conf
    * (Add this line below other IncludeOptional lines)

===== Create the MPM Event Module Config File =====
Create /etc/httpd/conf.d/mpm_event_module.conf with below lines
<code>
# event MPM
# ServerLimit: Default 16. 
# StartServers: initial number of server processes to start
# MinSpareThreads: minimum number of worker threads which are kept spare
# MaxSpareThreads: maximum number of worker threads which are kept spare
# ThreadsPerChild: constant number of worker threads in each server process
# MaxRequestWorkers: maximum number of worker threads
# MaxConnectionsPerChild: maximum number of connections a server process serves
#                         before terminating
# ThreadLimit: Sets the upper limit on the configurable number of threads per child process.  ThreadsPerChild can be modified during a restart up to the value of this directive.
<IfModule mpm_event_module>
    ServerLimit               16
    StartServers               3
    MinSpareThreads           75
    MaxSpareThreads          250
    ThreadLimit               64
    ThreadsPerChild           25
    MaxRequestWorkers        400
    MaxConnectionsPerChild  8000
</IfModule>
</code>


For 8,000 concurrent connections use this configuration.
<code>
<IfModule mpm_event_module>
    ServerLimit              250
    StartServers              10
    MinSpareThreads           75
    MaxSpareThreads          250 
    ThreadLimit               64
    ThreadsPerChild           32
    MaxRequestWorkers       8000
    MaxConnectionsPerChild 10000
</IfModule>
</code>

Ref: https://oxpedia.org/wiki/index.php?title=Tune_apache2_for_more_concurrent_connections