@DieterWerner
With respect to
I wonder if nobody uses or knows it
it is probably safe to say that the above
can be true - for a peculiar reason though.
Nginx, as shipped with Plesk, should not contain the ngx_http_limit_req_module - you can verify this with the command : nginx -V
However, as far as I know, you can simply declare the
limit_req_zone directive, without resulting in errors at config check (via the command : nginx -t ).
I do not (yet) know whether it can be recommended to use the
limit_req_zone directive, I still have to find time to get some decent checks designed and executed.
It could work though, so that is the good news - but you can imagine by now that the output of Nginx -V obfuscates the potential usage of the
limit_req_zone directive.
Anyway, you should note that - in general - it is a better idea to keep bad traffic from entering the proxy level (Nginx) or the webserver level (Apache) : also use a firewall!
Kind regards.........