A quick node.js script to do many pings to a load-balanced app until a given instance behind the load-balancer replies. Please note that I'm barely starting to use node.js, any improvement is most welcome.

app.coffee

express = require 'express'
rest = require 'restler'

app = express()

# a little url expected to return a x-commit header with the hostname
url = process.env.MONITORED_URL

attempts = 4

app.get '/', (req, res) =>
  res.send("OK")

app.get '/check/service/:id', (req, res) ->
  wanted_host = "my-app-default-#{req.params.id.replace ".", "-"}"
  remaining = attempts

  scan = (complete) =>
    rest.get(url).on 'complete', complete

  complete = (data, response) =>
    commit = response.headers['x-commit']
    host = commit && commit.split(',')[0] 
    if host == wanted_host
      res.send(200, "#{host} is up!")
    else
      remaining -= 1
      if remaining < 1
        res.send(500, "#{wanted_host} cannot be reached!")
      else
        scan(complete)

  scan(complete)

port = process.env.PORT || 5000

app.listen port

console.log "Server started on port #{port}" 

package.json

{
  "name": "node-example",
  "version": "0.0.1",
  "dependencies": {
    "express": "3.x",
    "coffee-script": "1.4.x",
    "restler": "2.0.1"
  },
  "devDependencies": {
    "supervisor": "0.5.0"
  },
  "engines": {
    "node": "0.8.x",
    "npm": "1.1.x"
  }
}

Procfile

web: node run.js

run.js

require("coffee-script");
require("./app.coffee");