demo-proxy.js

var proxy = require("http-proxy");

function proxy_couchdb(req, res, proxy) {

  var random_port = Math.random() >= 0.5 ?
    4444 : 5555;
  console.log("Proxy to %d", random_port);

  proxy.proxyRequest(req, res, {
    host: '127.0.0.1',
    port: random_port
  });
}

proxy.createServer(proxy_couchdb).listen(3333);