limit_conn is not limiting the number of connections in my use case

[matt_l]

Hello,

I have a hard time understanding limit_conn

My NGINX has the configuration below. I would expect to see 16 connections
on the backend server 192.168.10.131 defined in the "dynamic" directive. 

Yet I see ~50-60 connections.

QPS:                    3056
Active connections:     58
QPS:                    3064
Active connections:     54
QPS:                    3063
Active connections:     59

Please note the QPS (Query Per Second) limiting works well.

I would greatly appreciate any tip as to what is going on with my use of the
limit_conn.

Thank you.

upstream locallayer {
    server 127.0.0.1:7999;
    keepalive 32;
}
        
server {
    listen 8002;
    proxy_intercept_errors on;

    location / {
        proxy_http_version 1.1;
        proxy_set_header Connection "";
        proxy_pass http://locallayer;
    }
    error_page 302 400 403 404 408 500 502 503 504 = /empty;
    location /empty {
        return 204;
    }
}

upstream dynamic {
    least_conn;
    server 192.168.10.131:9990; 
    keepalive 32;
}
        
limit_conn_zone $binary_remote_addr zone=peripconn:100m;
limit_conn_zone $server_name zone=perserver:10m;
limit_req_zone $binary_remote_addr zone=peripreq:1000m rate=3000r/s;
        
server {
    listen 7999;
    server_name local.com;
    proxy_intercept_errors on;
    location / {
        allow 127.0.0.1;
        deny all;
        limit_conn peripconn 32;
        limit_conn perserver 32;
        limit_req zone=peripreq burst=100 nodelay;
        limit_conn_status 503;
        limit_req_status 503;
        proxy_http_version 1.1;
        proxy_set_header Connection "";
        proxy_connect_timeout 10ms;
        proxy_send_timeout 10ms;
        proxy_read_timeout 60ms;
        proxy_pass http://dynamic;
    }
    error_page 302 400 403 404 408 500 502 503 504 = /empty;
    location /empty {
        return 204;
    }
}

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,267688,267688#msg-267688