Why Nginx rate limit is not rejecting exceeded requests?

Question

This is my nginx configuration:

{
    # on top of conf file
    limit_req_zone $binary_remote_addr zone=main:10m rate=1r/s;  
    ...

    location /login {
            limit_req zone=main burst=3 nodelay;
            ModSecurityEnabled on;
            ModSecurityConfig /usr/local/nginx/conf/modsecurity.conf;
            proxy_pass http://localhost:4000;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection 'upgrade';
            proxy_set_header Host $host;
            proxy_cache_bypass $http_upgrade;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }

}

When hitting the api url (http://localhost:4000/login) multiple times using following code -

for i in {0..2000}; do (curl -Is http://localhost:4000/login | head -n1 &) 2>/dev/null; done

I am getting always getting 200 response code instead of getting 503 for some requests which should be rejected. Why is this happening?

Answer 1

This is my config. Now it is correctly displaying the 200 & 503 requests after passign tthe threshold.

limit_req_zone $http_x_forwarded_for zone=req_limit_per_ip:100m rate=10r/m;
limit_conn_zone $http_x_forwarded_for zone=conn_limit_per_ip:100m;


server {

listen 80;

server_name *.xxxxxx.com;
add_header 'Access-Control-Allow-Headers' "X-Forwarded-For; X-Forwarded-Proto; X-Forwarded-Port; Host; X-Amzn-Trace-Id; Connection";
#add_header 'Access-Control-Allow-Headers' "X-Requested-With";
add_header 'Access-Control-Allow-Methods' "GET, POST, OPTIONS";
#add_header 'Access-Control-Allow-Origin' "$http_origin";

server_tokens off;
client_body_timeout 60s;
client_header_timeout 60s;
add_header 'X-Frame-Options' "SAMEORIGIN";
add_header 'Strict-Transport-Security' "max-age=31536000; includeSubDomains" ;

location /api/ {
    ModSecurityEnabled off;
    ModSecurityConfig /usr/local/nginx/conf/modsecurity.conf;
    limit_req zone=req_limit_per_ip burst=10 nodelay;
    proxy_pass http://xx.xxx.xxx.xxx:7000/;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';
    proxy_set_header Host $host;
    proxy_cache_bypass $http_upgrade;
    proxy_connect_timeout       60s;
    proxy_send_timeout          60s;
    proxy_read_timeout          60s;
    send_timeout                60s;

}
}

To check the effect, I created a .js file and requested the above url 20 times inside a loop. You can check the results below -

Output:

Answer 2

For me limit_req was not working too. The issue was in wrong ordering - limit_req should come before proxy_pass

Works:

limit_req_zone $binary_remote_addr zone=req_limit_per_ip:10m rate=5r/s;

server {
  listen      443;
  server_name example.com;

  limit_req zone=req_limit_per_ip burst=10 nodelay;

  location / {
    proxy_pass         http://be_server;
  }
}

Works

limit_req_zone $binary_remote_addr zone=req_limit_per_ip:10m rate=5r/s;

server {
  listen      443;
  server_name example.com;

  location / {
    limit_req zone=req_limit_per_ip burst=10 nodelay;

    proxy_pass         http://be_server;
  }
}

Doesn't work

limit_req_zone $binary_remote_addr zone=req_limit_per_ip:10m rate=5r/s;

server {
  listen      443;
  server_name example.com;

  location / {
    proxy_pass         http://be_server;

    limit_req zone=req_limit_per_ip burst=10 nodelay;
  }
}