This blog post will show you how to setup PHP FPM on-demand child workers in PHP 7.x to increase website traffic.

My blog was experiencing a number of slow page loads and often running “sudo service php7.0-fpm restart” would resolve the problem.  I have blogged before about setting up Ubuntu Servers on AWS, Digital Ocean and Vultr but this post is about debugging and speeding up PHP on Ubuntu self-managed servers.

Background

I tried the normal tweaks in “/etc/php/7.0/fpm/php.ini” like

memory_limit = 512M

I setup servers like this.

Temporary Fix

I had even set up a temporary NGINX and php7.0-fpm restart ever 5 and 1-minute respectively until I had time to look into this.

*/5 * * * * /etc/init.d/nginx restart
* * * * * sudo service php7.0-fpm restart

Debug

I checked out the PHP7.0-fpm.log and I found the following

[25-Feb-2018 16:35:35] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it
[25-Feb-2018 17:02:26] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it
[25-Feb-2018 17:51:09] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it
[25-Feb-2018 18:18:51] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it
[25-Feb-2018 20:58:12] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it
[25-Feb-2018 21:02:57] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it
[25-Feb-2018 21:30:58] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it
[25-Feb-2018 21:35:10] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it
[25-Feb-2018 23:36:28] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it

Setting up a PHP-FPM pool

Read the official guide here on configuring PHP FPM pools etc.

I edited “/etc/php/7.0/fpm/pool.d/www.conf” and added the following to set up a pool of PHP-FPM servers.

; Note: This value is mandatory.
pm = dynamic

; The number ocf child processes to be created when pm is set to 'static' and the
; maximum number of child processes when pm is set to 'dynamic' or 'ondemand'.
; This value sets the limit on the number of simultaneous requests that will be
; served. Equivalent to the ApacheMaxClients directive with mpm_prefork.
; Equivalent to the PHP_FCGI_CHILDREN environment variable in the original PHP
; CGI. The below defaults are based on a server without much resources. Don't
; forget to tweak pm.* to fit your needs.
; Note: Used when pm is set to 'static', 'dynamic' or 'ondemand'
; Note: This value is mandatory.
pm.max_children = 40

; The number of child processes created on startup.
; Note: Used only when pm is set to 'dynamic'
; Default Value: min_spare_servers + (max_spare_servers - min_spare_servers) / 2
pm.start_servers = 10

; The desired minimum number of idle server processes.
; Note: Used only when pm is set to 'dynamic'
; Note: Mandatory when pm is set to 'dynamic'
pm.min_spare_servers = 5

; The number of seconds after which an idle process will be killed.
; Note: Used only when pm is set to 'ondemand'
; Default Value: 10s
pm.process_idle_timeout = 30s;

; The number of requests each child process should execute before respawning.
; This can be useful to work around memory leaks in 3rd party libraries. For
; endless request processing specify '0'. Equivalent to PHP_FCGI_MAX_REQUESTS.
; Default Value: 0
pm.max_requests = 250

You may need more or fewer child processes depending on your needs and free memory.

After editing the PHP-FPM config file restart PHP-FPM

sudo service php7.0-fpm restart

Restart Nginx

sudo /etc/init.d/nginx restart

You will be able to view the PHP child process status by typing the following

service php7.0-fpm status
● php7.0-fpm.service - The PHP 7.0 FastCGI Process Manager
   Loaded: loaded (/lib/systemd/system/php7.0-fpm.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2018-02-26 00:33:17 AEDT; 5min ago
     Docs: man:php-fpm7.0(8)
 Main PID: 1284 (php-fpm7.0)
   Status: "Processes active: 0, idle: 10, Requests: 56, slow: 0, Traffic: 0.2req/sec"
    Tasks: 11
   Memory: 330.1M
      CPU: 39.558s
   CGroup: /system.slice/php7.0-fpm.service
           ├─1284 php-fpm: master process (/etc/php/7.0/fpm/php-fpm.conf)
           ├─1503 php-fpm: pool www
           ├─1504 php-fpm: pool www
           ├─1505 php-fpm: pool www
           ├─1506 php-fpm: pool www
           ├─1507 php-fpm: pool www
           ├─1508 php-fpm: pool www
           ├─1509 php-fpm: pool www
           ├─1511 php-fpm: pool www
           ├─1512 php-fpm: pool www
           └─1513 php-fpm: pool www

Feb 25 10:33:16 servername systemd[1]: Starting The PHP 7.0 FastCGI Process Manager...
Feb 25 10:33:17 servername systemd[1]: Started The PHP 7.0 FastCGI Process Manager.

You can use htop (commands here) to see child PHP processes in the pool and to verify free memory.

This command is good for watching free memory on a server

watch -n 1 'free -m'

I prefer to use up free memory (if available) and leave about 100mb free.

Every 1.0s: free -m                                                                                                            Mon Feb 26 00:47:55 2018

              total        used        free      shared  buff/cache   available
Mem:            992         518         120          40         353         280
Swap:             0           0           0

Hope this helps someone.

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