PHP: server reached pm.max_children

Sudden received a question from Colleagues.

They could not visit the website when many members visiting it together for demo.

Reviewed the logs.

Identified /var/log/php5.7-fpm.log
[28-Jul-2021 19:48:33] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it
[28-Jul-2021 19:58:10] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it
[28-Jul-2021 20:11:45] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it


Edit /etc/php/5.6/fpm/pool.d/www.conf

Original:
pm = dynamic
pm.max_children = 5
pm.start_servers = 2
pm.min_spare_servers = 1
pm.max_spare_servers = 3
pm.max_request = 500


Solved the question by    
pm.max_children = 40


Not related to Rate Limiting with Nginx

/var/log/nginx/error.log, it did not have any related.



References
https://www.php.net/manual/en/install.fpm.configuration.php


Update