How do I shutdown a Node.js http(s) server immediately?

The trick is that you need to subscribe to the server's connection event which gives you the socket of the new connection. You need to remember this socket and later on, directly after having called server.close(), destroy that socket using socket.destroy().

Additionally, you need to listen to the socket's close event to remove it from the array if it leaves naturally because its keep-alive timeout does run out.

I have written a small sample application you can use to demonstrate this behavior:

// Create a new server on port 4000
var http = require('http');
var server = http.createServer(function (req, res) {
  res.end('Hello world!');
}).listen(4000);

// Maintain a hash of all connected sockets
var sockets = {}, nextSocketId = 0;
server.on('connection', function (socket) {
  // Add a newly connected socket
  var socketId = nextSocketId++;
  sockets[socketId] = socket;
  console.log('socket', socketId, 'opened');

  // Remove the socket when it closes
  socket.on('close', function () {
    console.log('socket', socketId, 'closed');
    delete sockets[socketId];
  });

  // Extend socket lifetime for demo purposes
  socket.setTimeout(4000);
});

// Count down from 10 seconds
(function countDown (counter) {
  console.log(counter);
  if (counter > 0)
    return setTimeout(countDown, 1000, counter - 1);

  // Close the server
  server.close(function () { console.log('Server closed!'); });
  // Destroy all open sockets
  for (var socketId in sockets) {
    console.log('socket', socketId, 'destroyed');
    sockets[socketId].destroy();
  }
})(10);

Basically, what it does is to start a new HTTP server, count from 10 to 0, and close the server after 10 seconds. If no connection has been established, the server shuts down immediately.

If a connection has been established and it is still open, it is destroyed. If it had already died naturally, only a message is printed out at that point in time.

I found a way to do this without having to keep track of the connections or having to force them closed. I'm not sure how reliable it is across Node versions or if there are any negative consequences to this but it seems to work perfectly fine for what I'm doing. The trick is to emit the "close" event using setImmediate right after calling the close method. This works like so:

server.close(callback);
setImmediate(function(){server.emit('close')});

At least for me, this ends up freeing the port so that I can start a new HTTP(S) service by the time the callback is called (which is pretty much instantly). Existing connections stay open. I'm using this to automatically restart the HTTPS service after renewing a Let's Encrypt certificate.

If you need to keep the process alive after closing the server, then Golo Roden's solution is probably the best.

But if you're closing the server as part of a graceful shutdown of the process, you just need this:

var server = require('http').createServer(myFancyServerLogic);

server.on('connection', function (socket) {socket.unref();});
server.listen(80);

function myFancyServerLogic(req, res) {
    req.connection.ref();

    res.end('Hello World!', function () {
        req.connection.unref();
    });
}

Basically, the sockets that your server uses will only keep the process alive while they're actually serving a request. While they're just sitting there idly (because of a Keep-Alive connection), a call to server.close() will close the process, as long as there's nothing else keeping the process alive. If you need to do other things after the server closes, as part of your graceful shutdown, you can hook into process.on('beforeExit', callback) to finish your graceful shutdown procedures.