Here is a quick guide to help you resolve the server reached max_children setting error. Our Plesk Support team is here to lend a hand with your queries and issues.

Server reached max_children setting Error : Causes & Fixes

Some of our customers who have websites with the PHP handler set to FPM application served by Apache or FPM application served by Nginx at Domains > example.com > PHP Settings have been experiencing the following errors:

• Websites load slowly.
• One of the following error messages appears:

  502 Bad Gateway
  503 Service Temporarily Unavailable
  504 Gateway Time-out
• The following warning message appears in the PHP-FPM error log file:

  WARNING: [pool example.com] server reached max_children setting (*), consider raising it.
• In case Nginx is enabled on the server, we may come across one of the following error messages in the domain’s error log file.

According to our experts, the root cause behind the server reaching max_children setting is because the PHP-FPM pm.max_children value has hit the set value by the website. Fortunately, we can quickly resolve the error by increasing the limit pm.max_children limit for the affected website.

1. To begin with, we have to connect to Plesk through SSH.
2. Then, we can find the affected website with the following command:

   grep -r "server reached max_children setting" /var/log/*php*-fpm/error.log /var/www/vhosts/system/*/logs/php-fpm_error.log | cut -d' ' -f5 | tr -d ']' | sort | uniq -c | sort -nr
3. Next, log in to Plesk and navigate to Domains > example.com > PHP Settings > PHP-FPM Settings.
4. At this point, we can easily change the pm.max_children value for the website we got as an output in Step 2.

Alternatively, we can increase the pm.max_children limit via CLI with the following steps:

1. First, we have to create a php.ini file in the domain’s system directory as seen below:

   touch /var/www/vhosts/system/example.com/conf/php.ini
2. Next, open this file and add the following:

   [php-fpm-pool-settings]
pm.max_children = 20

3. Now, we have to save the changes and exit.
4. Finally, run this command to apply the changes:

   /usr/local/psa/bin/php_settings -u

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Conclusion

In summary, our Support Techs demonstrated the root cause behind the server reached max_children setting error and how to easily resolve it.