php-fpm error 503 and website loading issues

Hi,
when working with php-fpm, in both apache and nginx we have some servers that send permanent or random 503 errros
or just not load the site, for 503 move to mod_php solve the issues
for not load, restart the php-fpm solve the issue

It's just unstable? configuration issues?
thy option to compile with lsphp with Apache or Nginx like cPanel?

Regards,

Hello,

If you increase pm.max_children will it help?