Yes, you're right, it's just a DoS attack xD
I would like to thank you for the links, I will review it!
In fact, technically speaking, the server does not fall. However, it stops responding to HTTP requests.
Yes, I made the attacks with the mitigation and the firewall running.
As I said,
I am running a simple NGINX + MariaDB + PHP 7.2 on CentOS 7 with a WordPress website.
If you know something you can do, your help is welcome!
I can not believe that they have blocked me, because this happened from the first moment.
I also took some precautions to not expose my real IP.