Error 500 on sites and log file shows "failed to open stream: Permission denied in"

Symptoms

A PHP website is showing error 500 and /var/log/apache2/error_log reports "failed to open stream: Permission denied in".

Description 

The file being accessed while using CGI is strict because the file permissions may be set to 640 which means it's only readable as the user.

Example:

 ls -al /home/someuser/public_html/wp-config.php
-rw-r----- 1 someuser someuser 3612 May 26 21:22 /home/someuser/public_html/wp-config.php

Without suexec or ruid2 the Apache error_log will report the following when trying to load the site:

AH01215: PHP Fatal error: require_once(): Failed opening required '/home/someuser/public_html/wp-config.php' (include_path='.:/opt/cpanel/ea-php74/root/usr/share/pear') in /home/someuser/public_html/wp-load.php on line 37: /usr/local/cpanel/cgi-sys/ea-php74, referer: https://someuserssite.com/

Workaround

An Apache module of either mod_suexec or mod_ruid2 needs to be installed.

mod_suexec can be installed with:

yum install ea-apache24-mod_suexec

mod_ruid2 can be installed with

yum install ea-apache24-mod_ruid2

We have more information on mod_ruid2 and mod_suexec at:

mod_ruid2 vs mod_suexec