Setting Up Nginx + PHP-FPM to handle 1000 Connections !simultaneously!

Hello,

I'm trying to setting up nginx + php-fpm to handle many connections simultaneously but i can't.
My Current Config of nginx.conf is the following

user www-data;
worker_processes 8;
worker_rlimit_nofile 150000;
pid /run/nginx.pid;
events {
worker_connections 150000;
multi_accept on;
use epoll;
}


http {
.......
}


My php pool config is the following:

pm = ondemand
pm.max_children = 4000


I tried to set pm as static/dynamic but nothing of them worked properly. Even if i setted that to: ondemand and max_children 4000 always nginx crashes at ~400 Open connections.

I always get something like 400-430 Connections and it can't handle more. I get Bad Gateway error after that and the connections are being closed.

Thank you
Hope you understand