This is an example NGINX configuration for the blog: Performing A/B Testing with NGINX - This demonstrates split_clients based routing on an argument named token

nginx.conf

user  nginx;
worker_processes  auto;
error_log  /var/log/nginx/error.log info;
pid        /var/run/nginx.pid;
events { worker_connections  1024; }
http {
        default_type  text/html;
        log_format  main  '$remote_addr -> $request     $status $body_bytes_sent bytes -> $upstream_addr';
        access_log  /var/log/nginx/access.log  main;

        upstream version_1a {
                server 127.0.0.1:3001;
        }

        upstream version_1b {
                server 127.0.0.1:4001;
        }

        split_clients "${arg_token}" $dynamic {
                95%     version_1a;
                *       version_1b;
        }

        server {
                listen 3001;
                location / {
                        return 200 "Token: $arg_token\t\tServed from site $dynamic. \n";
                }
        }

        server {
                listen 4001;
                location / {
                        return 200 "Token: $arg_token\t\tServed from site $dynamic!! \n";
                }
        }

        server {
                listen 80;
                location / {
                        proxy_set_header Host $host;
                        proxy_pass http://$dynamic;
                }
        }
}