I had to handle high-traffic loads a few months ago for my client and we were going through with downtime, not using memory, and a lot of trouble in my past. In this article, I want to give a step-by-step guide to apache2 performance settings, which is a concentrated result of a lot of reading and trying.

My environment

• AWS EC2 (m4.xlarge): 4 *2,4GHz | 16GB RAM
• Ubuntu 16.04
• Apache 2.4 using mpm_event
• PHP FPM (5.6, 7.4)

Precalculation of average memory usage and max clients/max-children

1. Calculate process size

You need to know how many processes can run on your machine. So calculating the process size of your main CPU/memory drivers is necessary.

There are several calculation methods out there. Personally, I prefer this Python script as it takes shared memory into account and will give insights into actual memory usage.

cd ~
wget https://raw.githubusercontent.com/pixelb/ps_mem/master/ps_mem.py
chmod a+x ps_mem.py
sudo python ps_mem.py

ps_mem.py will produce output like this:

Here you can see that there are 30 apache2 processes, consuming a total of 139MiB, so each Apache process uses roughly 5MiB of RAM. The PHP-fpm5.6 process will use about 50MiB.

2. Calculate Apache MaxRequestWorkers

To be safe though, I’ll reserve 15% of memory for all other processes (in my case ~2,4GiB) and round up Apache process size to 5MiB.

MaxRequestWorkers = (Total RAM - Memory used for Linux, DB, etc.) / process size
MaxRequestWorkers = (16384MB - 2400MB) / 5MB = 2800

3. Calculate php-fpm max-children

To be safe though, I’ll reserve 1 GiB for all other processes and round up the php process size to 55MiB.

maxclients = (Total RAM - Memory used for Linux, DB, etc.) / process size
maxclients = (16384MB - 2400MB) / 55MB = 256

I found, this Excel Sheet for the calculation: https://s3.buckpesch.io/downloads/apache_performance.xlsx

Detailed Setup

In the /etc/apache2/mods-enabled/mpm-event.conf or /etc/apache2/mods-enabled/mpm-worker.conf file:

<IfModule mpm_*_module>
  ServerLimit           (Total RAM - Memory used for Linux, DB, etc.) / process size
  StartServers          (Number of Cores)
  MinSpareThreads       25
  MaxSpareThreads       75
  ThreadLimit           64
  ThreadsPerChild       25
  MaxRequestWorkers     (Total RAM - Memory used for Linux, DB, etc.) / process size
  MaxConnectionsPerChild   1000
</IfModule>

Note that the default settings did not contain the “ServerLimit”, so I added it here.

In the /etc/php/7.4/fpm/pool.d/www.conf change the following locations:

pm = dynamic            
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)
pm.max_requests         1000

To learn about all php-fpm settings I recommend watching the video on that page: https://serversforhackers.com/c/php-fpm-process-management

My final settings

My server has 16GB RAM and 4 CPUs à 2,4GHz. My average apache process has 5MB, and an average PHP process takes 55MB.

/etc/apache2/mods-available/mpm_event.conf

# Optimized settings for avg. apache process 15MB and AWS EC2 m4.xlarge Server
<IfModule mpm_event_module>
        ServerLimit              2800
        StartServers             4
        MinSpareThreads          25
        MaxSpareThreads          75
        ThreadLimit              64
        ThreadsPerChild          25
        MaxRequestWorkers        2800
        MaxConnectionsPerChild   1000
</IfModule>

/etc/php/7.4/fpm/pool.d/www.conf

; Optimized for php-fpm request size of 55MB on AWS EC2 m4.xlarge (4CPU cores, 16GB RAM)
pm = dynamic
pm.max_children = 256
pm.start_servers = 20
pm.min_spare_servers = 10
pm.max_spare_servers = 20
pm.max_requests = 1000

Save your settings and restart your Apache and php-fpm processes

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

Also, read Enable HTTP/2 with Apache in Ubuntu 2023

Test you settings

To test your server settings you can run Apache Bench tests and see how your server behaves in htop .

Open 2 terminals and the following command to test 5000 requests with a concurrency of 100 parallel requests:

ab -n 5000 -c 100