config.ru

port = lambda do |env|
  body = "Hello from variant #{ENV['VARIANT']} on #{env['SERVER_NAME']}:#{env['SERVER_PORT']} at #{env['HTTP_X_TIME']}"
  [200, {"Content-Type" => "text/html"}, [body]]
end
 
run port

splitter.conf

worker_processes 1;

events {
    worker_connections  1024;
}

http {

    access_log /home/dave/scrap/nginx-split/access.log;
    error_log  /home/dave/scrap/nginx-split/error.log;

    upstream _a {
        server 127.0.0.1:8000;
    }

    upstream _b {
        server 127.0.0.1:8001;
    }

    upstream _c {
        server 127.0.0.1:8002;
    }

    # Chain of upstream conditions
    # ----------------------------
    # In order of preference, set upstream by:
    # - url parameter
    # - cookie
    # - random
    
    split_clients $date_gmt $random_splitter {
        10% _a;
        10% _b;
        80% _c;
    }

    map $cookie__v $cookie_upstream {
        '_a' _a;
        '_b' _b;
        '_c' _c;
        default $random_splitter;
    }
    
    map $arg__v $upstream {
        '_a' _a;
        '_b' _b;
        '_c' _c;
        default $cookie_upstream;
    }

    # EOF of upstream conditions

    server {

        listen 80;
        server_name localhost;

        location / {
            proxy_pass http://$upstream$request_uri;
            proxy_pass_request_headers on;
            proxy_set_header Host $host;
            add_header X-Time $date_gmt;
            proxy_set_header X-Time $date_gmt;
        }
    }

}