The server crashes from overloads due to fastcgi, what could be the problem?

Question

PHP

The virtual server has 2 cores, 4 GB of RAM, 15 domains and approximately 75 subdomains.
Several work on modx, subdomains are tied to one of the admins. all php is executed as cgi script.
The following error keeps popping up from the logs:
[error] mod_fcgid: process /var/www/php-bin/username/php(15316) exit(communication error), get unexpected signal 11
And the site crashes with a 502 response code.
Tell me what could be the problem?
If there is not enough memory, then what should be the limit in php.ini?

Answer 1

It seems to me yes, it's in memory and processor.
I didn’t exactly understand web servers, but in my opinion, when installing 128mb on 1 site * 15 domains, it will come out a lot. And you also have subdomains. So you yourself understand that the server simply cannot cope with such loads. Either put very little memory on allocation, or improve the server itself. You can also try caching.

Answer 2

11 code - segmentation error. Most likely a bug in some PHP module or library used. It is necessary to catch this either with a debugger, or with a scientific poke method.
It is not at all a fact that the problem is somehow related to the load, the power of the hardware, or the number of virtual hosts.

Answer 3

https://serverfault.com/questions/364341/500-error...
forum.directadmin.com/showthread.php?t=50002&page=...
www.remoteshaman.com/server/apache/pobezhdaem-oshi..
.shortly: Permissions
/htaccess/old modules in php