Quick and dirty zero-downtime process restart

zero-downtime.js

var http = require('http'),
    fork = require('child_process').fork;

var serverHandle, server;

function log(l) {
  console.log(process.pid + ': ' + l);
}

process.on('SIGUSR2', function () {
  log('rolling restart');

  var child = fork(__filename);
  child.send('handle', server._handle);
  child.on('message', function (m) {
    if (m === 'listening') {
      log('child listening, quitting');
      server.close();
    }
  });
});

if (process.send) {
  log('running as a child');
  process.on('message', function (m, handle) {
    if (m === 'handle') {
      serverHandle = handle;
    }
  });
}
else {
  serverHandle = 8000;
}

log('delaying server start...');
setTimeout(function () {
  log('server starting.');
  server = http.createServer(function (req, res) {
    log('request');
    res.end('Hello world, process id: ' + process.pid + '\n');
  });
  server.listen(serverHandle, function () {
    log('listening on ' + server.address().port);
    if (process.send) {
      process.send('listening');
    }
  });
}, 2048);