proxy_with_balance_file.js

var posix = require('posix'),
      sys = require('sys'),
     http = require('http');

http.createServer(function (req, res) {
  checkBalanceFile(req, res);
}).listen(8000);

function checkBalanceFile(req, res) {
  var promise = posix.stat("balance");
  promise.addCallback(function () {
    passThroughOriginalRequest(req, res);
  });
  promise.addErrback(function () {
    setTimeout(function() {checkBalanceFile(req, res)}, 1000);
  });
}

function passThroughOriginalRequest(req, res) {
  var request = http.createClient(2000, "localhost").request("GET", req.url, {});
  request.finish(function (response) {
    res.sendHeader(response.statusCode, response.headers);
    response.addListener("body", function (chunk) {
      res.sendBody(chunk);
    });
    response.addListener("complete", function () {
      res.finish();
    });
  });
}

sys.puts('Server running at http://127.0.0.1:8000/');