It’s important to know how to increase the limits for php-fpm www pools, or any other named alias pools you might have setup.

You might see an error like

tail -f /var/log/php7.1-fpm.log

[24-Apr-2017 11:23:09] WARNING: [pool www] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 8 children, there are 0 idle, and 11 total

or

[24-Apr-2017 10:51:38] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it

The solution is quite simple, we just need to go in and edit the php fpm configuration on the server and increase these values to safe ones that is supported by available RAM.

pm.max_children = 15

; 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 = 2

; 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 = 1

; The desired maximum number of idle server processes.
; Note: Used only when pm is set to 'dynamic'
; Note: Mandatory when pm is set to 'dynamic'
pm.max_spare_servers = 8

Then monitor the site with

tail -f /var/log/php7.1-fpm.log

To ensure no further limits are being hit.

Obviously if you are using different version of fpm your log location might be different.