Changing php-fpm ‘pm’ settings in App Service Wordpress on Linux

This post describes how to change php-fpm settings in Wordpress on App Service Linux.

Overview

Note: This is regarding the Wordress on Linux “marketplace” image and not about using a PHP 8.x “Blessed image” with a Wordpress installation. These are two different products.

Wordpress on App Service Linux Docker Images utilize php-fpm, which can have various settings be changed if needed. The current settings are set to generous defaults, notably the following which are some of the more popular ones:

pm.max_children = 50
pm.start_servers = 20
pm.min_spare_servers = 5
pm.max_spare_servers = 35

A typical reason for wanting to change some of these is if [pool www] server reached pm.max_children setting (50), consider raising it is seen. Although there are other core reasons why this is likely appearing aside from the fact that simply that max children php-fpm processes were hit. That is however outside of this post.

Configuration

The settings talked about here are found in zz-docker.conf under /usr/local/etc/php-fpm.d/zz-docker.conf. The default file contains the following currently:

[global]
daemonize = no

[www]
;listen = 9000
listen = /var/run/php/php-fpm.sock
listen.owner = nginx
listen.group = nginx
listen.mode = 0660

pm = dynamic
pm.max_children = 50
pm.start_servers = 20
pm.min_spare_servers = 5
pm.max_spare_servers = 35

Although www.conf has the same settings, changing this (even with reloading php-fpm and nginx) will not have php-fpm pick up these changes. This can be confirmed with the php-fpm -tt CLI command or, depending on what was changed (like pm.start_servers), you can use top or ps.

Rationale on why this file exists and may be used over www.conf can be found in this PHP-FPM GitHub thread - Documentation regarding configuration. - Issue #241

1. Through WebSSH in the application container, Copy over the existing zz-docker.conf file from /usr/local/etc/php-fpm.d/zz-docker.conf to /home/dev/.
2. Make the desired changes in zz-docker.conf. As an example, we’ll change pm.max_children to 40 and pm.start_servers to 10.

... other settings
pm = dynamic
pm.max_children = 40
pm.start_servers = 10
pm.min_spare_servers = 5
pm.max_spare_servers = 35
... other settings

1. Follow How to run Bash scripts in WordPress on Azure App Service (techcommunity) / How to run Bash scripts in WordPress on Linux App Services (GitHub) regarding the startup script location under /home/dev/startup.sh

2. Add the following to your /home/dev/startup.sh file:

#!/bin/bash

cp /home/dev/zz-docker.conf /usr/local/etc/php-fpm.d/
echo "Copied /home/dev/zz-docker to /usr/local/etc/php-fpm.d/"

You can confirm this was executed by running cat /tmp/post-startup-script-stdout---supervisor-xxxxxxxx.log

NOTE: If they are any errors with startup script execution they’ll be logged in /tmp/post-startup-script-stderr---supervisor-xxxxxxxx.log

1. Restart the site.
2. Validate the changes. Run php -tt, below is a truncated output example - we can our pm.max_children and pm.start_servers change:

[18-Jan-2024 18:46:49] NOTICE:  pm = dynamic
[18-Jan-2024 18:46:49] NOTICE:  pm.max_children = 40
[18-Jan-2024 18:46:49] NOTICE:  pm.start_servers = 10
[18-Jan-2024 18:46:49] NOTICE:  pm.min_spare_servers = 5
[18-Jan-2024 18:46:49] NOTICE:  pm.max_spare_servers = 35
[18-Jan-2024 18:46:49] NOTICE:  pm.max_spawn_rate = 32
[18-Jan-2024 18:46:49] NOTICE:  pm.process_idle_timeout = 10
[18-Jan-2024 18:46:49] NOTICE:  pm.max_requests = 500
[18-Jan-2024 18:46:49] NOTICE:  pm.status_path = undefined
[18-Jan-2024 18:46:49] NOTICE:  pm.status_listen = undefined

1. Next, again depending on what was changed, you can use top to validate this. Since pm.start_servers is a change you can easily visually see by the number of php-fpm child processes at “rest”, we can count the ones we see:

263   184 nginx    SN    594m  19%   0   0% php-fpm: pool www
266   184 nginx    SN    594m  19%   0   0% php-fpm: pool www
265   184 nginx    SN    594m  19%   0   0% php-fpm: pool www
184   182 root     SN    591m  18%   0   0% php-fpm: master process (/usr/local/etc/php-fpm.conf)
271   184 nginx    SN    591m  18%   0   0% php-fpm: pool www
264   184 nginx    SN    591m  18%   0   0% php-fpm: pool www
272   184 nginx    SN    591m  18%   0   0% php-fpm: pool www
270   184 nginx    SN    591m  18%   0   0% php-fpm: pool www
267   184 nginx    SN    591m  18%   0   0% php-fpm: pool www
268   184 nginx    SN    591m  18%   0   0% php-fpm: pool www
269   184 nginx    SN    591m  18%   0   0% php-fpm: pool www

We can confirm there is a default of 10 php-fpm child processes.

Knowing the above, other settings can be changed as needed in the zz-docker.conf file, although in most cases, this does not need to be done.