single.js

var cluster = require("cluster");
var http = require("http");

if(cluster.isMaster) {
  cluster.fork();

  testConnection();
  setInterval(testConnection, 1000);
} else {
  var server = http.createServer(function(req, res) {
    res.writeHeader(202);
    res.end();

    setTimeout(function() {
      server.listen(7070);
    }, 2000);
    server.close();
  });

  server.listen(7070);
}

function testConnection() {
  http.get("http://localhost:7070/", function(res) {
    printStatus(res.statusCode == 202);
  }).on("error", function() {
    printStatus(false);
  });
}

function printStatus(success) {
  var worker = cluster.workers[1];
  if(success) {
    process.stdout.write(".");
  } else {
    process.stdout.write("!");
  }

  if(!worker.isConnected() || worker.isDead()) {
    console.error("Worker dead or disconnected");
    process.exit(1);
  }
}