01_nginx.conf

worker_processes  1;

events {
    worker_connections  1024;
}


http {
    include       /home/t/nginx/conf/mime.types;
    default_type  application/octet-stream;

    sendfile        on;
    keepalive_timeout  65;

    userid on;
    userid_name vrid;
    userid_domain example.com;
    userid_expires max;

    split_clients "${uid_set}${uid_got}" $bucketid {
        10%      "bucketOne";
        *        "bucketTwo";
    }    

    upstream @appone {
       server 0.0.0.0:3000;
    }

    server {
        listen       80;
        server_name  localhost;

        location / {
           proxy_set_header X-Bucket-ID $bucketid;
           add_header X-Bucket-ID $bucketid;
           proxy_pass http://@appone;
        }
    }
}

02_response.txt

[jmervine@jmervine01 ~]$ curl localhost -i
HTTP/1.1 200 OK
Server: nginx/1.4.2
Date: Thu, 25 Jul 2013 05:58:46 GMT
Content-Type: text/plain
Transfer-Encoding: chunked
Connection: keep-alive
X-Bucket-ID: bucketTwo
Set-Cookie: vrid=fwAAAVHwvpZmaHXrAwMFAg==; expires=Thu, 31-Dec-37 23:55:55 GMT; domain=example.com; path=/

Hello bucketTwo
[jmervine@jmervine01 ~]$ curl localhost -i
HTTP/1.1 200 OK
Server: nginx/1.4.2
Date: Thu, 25 Jul 2013 05:58:52 GMT
Content-Type: text/plain
Transfer-Encoding: chunked
Connection: keep-alive
X-Bucket-ID: bucketOne
Set-Cookie: vrid=fwAAAVHwvpxmaHXrAwMGAg==; expires=Thu, 31-Dec-37 23:55:55 GMT; domain=example.com; path=/

Hello bucketOne

zz_app.js

var http = require('http');

var server = http.createServer(function (request, response) {
  response.writeHead(200, {"Content-Type": "text/plain"});
  var bucketId = request.headers['x-bucket-id'];
  response.end("Hello "+bucketId+"\n");
});

server.listen(3000);
console.log("Server running at http://127.0.0.1:3000/");