Nginx # limit_conn limit_per_ip 16; ssi on;

for Centmin Mod it's in reference to commented out line 101 in nginx.conf https://github.com/centminmod/centminmod/blob/master/config/nginx/nginx.conf#L101

Code:

#######################################
# use limit_conn_zone for Nginx >v1.1.8 and higher
# limit_conn_zone $binary_remote_addr zone=limit_per_ip:16m;
#######################################

and is number of connections per IP address, not IP addresses per connection

so probably not suited for your usage

see http://nginx.org/en/docs/http/ngx_http_limit_conn_module.html#limit_conn

Syntax:limit_conn zone number;
Default:—
Context:http, server, location

Sets the shared memory zone and the maximum allowed number of connections for a given key value. When this limit is exceeded, the server will return the 503 (Service Temporarily Unavailable) error in reply to a request. For example, the directives

Code:

limit_conn_zone $binary_remote_addr zone=addr:10m;

server {
location /download/ {
limit_conn addr 1;
}

allow only one connection per an IP address at a time.

When several limit_conn directives are specified, any configured limit will apply. For example, the following configuration will limit the number of connections to the server per a client IP and, at the same time, the total number of connections to the virtual host:

Code:

limit_conn_zone $binary_remote_addr zone=perip:10m;
limit_conn_zone $server_name zone=perserver:10m;

server {
...
limit_conn perip 10;
limit_conn perserver 100;
}

 

2nd post in this thread has the example and Module ngx_http_limit_conn_module

for example limit 30 connections per IP address

nginx.conf

Code:

http {
limit_conn_zone $binary_remote_addr zone=addr:10m;

vhost file

Code:

server {
location /download/ {
    limit_conn addr 30;
}

or limit to 150 requests/second per IP address with burst size 200 50 (point at which 503 errors are shown) Module ngx_http_limit_req_module

nginx.conf

Code:

http {
limit_req_zone $binary_remote_addr zone=one:10m rate=120r/s;

vhost file

Code:

location /search/ {
    limit_req zone=one burst=50;
}

 

yes on root location context /

but might be better to limit requests to PHP itself via /usr/local/nginx/conf/php.conf (cmd short = phpinc) include file see example Nginx Flood Protection with Limit_req » KBeezie as Nginx static files can handle alot more compared to PHP requests via PHP-FPM

edited above to burst size 200 50