PHP-FPM Optimization

Out-of-box php fpm is configured for very low server specs such as a 2 core machine. It needs to be configured to match the hardware you are on. You need to factor on the most expensive processes you run.

Typically a low-end production server has 4 cores with 8 GB RAM so you can use the following configuration:

Edit the file /etc/apache2/mods-enabled/mpm-event.conf and add the following:

# event MPM
# 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 requests a server process serves
# <IfModule mpm_event_module>
# 	StartServers			 2
# 	MinSpareThreads		 25
# 	MaxSpareThreads		 75
# 	ThreadLimit			 64
# 	ThreadsPerChild		 25
# 	MaxRequestWorkers	  150
# 	MaxConnectionsPerChild   0
# </IfModule>


#  ServerLimit           (Total RAM - Memory used for Linux, DB, etc.) / process size
#  StartServers          (Number of Cores)
#  MaxRequestWorkers     (Total RAM - Memory used for Linux, DB, etc.) / process size

<IfModule mpm_event_module>
        # for c5 classes with only 8GB ram
        # ServerLimit              500
        StartServers             4
        MinSpareThreads          25
        MaxSpareThreads          75
        ThreadLimit              64
        ThreadsPerChild          25
        MaxRequestWorkers        2800
        # for c5 classes with only 8GB ram
        # MaxRequestWorkers       1400
        MaxConnectionsPerChild   1000
</IfModule>

Edit the file /etc/php/7.4/fpm/pool.d/www.conf and make sure the following setting are there:

; settings explanation - don't need to copy this     
;pm.max_children         (total RAM - (DB etc) / process size)
;pm.start_servers        (cpu cores * 4)
;pm.min_spare_servers    (cpu cores * 2)
;pm.max_spare_servers    (cpu cores * 4)


; default is dynamic but that can churn up the memory because it leave processes lingering
; pm = dynamic
pm = ondemand
; default is pm.max_children = 5
pm.max_children = 256

; everything below is only relevant if using pm = dynamic
; for c class servers with only 8GB ram
; pm.max_children = 128
; default is pm.start_servers = 2
pm.start_servers = 16
; default is pm.min_spare_servers = 1
pm.min_spare_servers = 8
; default is pm.max_spare_servers = 3
pm.max_spare_servers = 16
; setting to 0 or leaving commented out will use the PHP_FCGI_MAX_REQUESTS value whatever that is.
pm.max_requests = 1000

Now we have allowed php to run a lot more threads we may run into a “too many open files” error.

To fix edit /etc/php/7.4/fpm/php-fpm.conf and change the rlimit_files to 4096. If you are still getting the “too many open files” error you can double this.

rlimit_files = 10000

You can also try editing /etc/security/limits.conf and adding the following:

*              hard    nofile      10000
*              soft    nofile      10000
www-data       soft    nofile  10000
www-data       hard    nofile  10000

Restart everything:

sudo service apache2 restart && sudo service php7.4-fpm restart