I have the classical LAMP configuration on several servers, on one server I can frequently see Apache returned an empty error.
I have PHP-FPM running to serve .php file, static pages like .html is okay however if I keep the server running for 1 day, .php will be inaccessible and returned empty response, I must restart httpd to recover this issue.
I can see the only error log in Apache is:
[:error] [pid 21153] ModSecurity: ModSecurity requires mod_unique_id to be installed.
However I have same configuration on other servers, both got this error but did not have this issue.
How should I diagnose this issue?
Thanks in advance.