Efficient HTTP shutdown with keepalives?

Question

Efficient HTTP shutdown with keepalives?

This Node.js server will shutdown cleanly on a Ctrl+C when all connections are closed.

var http = require('http');
var app = http.createServer(function (req, res) {
  res.end('Hello');
});

process.on('SIGINT', function() {
  console.log('Closing...');
  app.close(function () {
    console.log('Closed.');
    process.exit();
  });
});

app.listen(3000);

The problem with this is that it includes keepalive connections. If you open a tab to this app in Chrome and then try to Ctrl+C it, it won't shutdown for about 2 minutes when Chrome finally releases the connection.

Is there a clean way of detecting when there are no more HTTP requests, even if some connections are still open?

node.js
http

Answer 1

You can hack some request tracking with the finish event on response:

var reqCount = 0;

var app = http.createServer(function (req, res) {
  reqCount++;
  res.on('finish', function() { reqCount--; });
  res.end('Hello');
});

Allowing you to check whether reqCount is zero when you come to close the server.

The correct thing to do, though, is probably to not care about the old server and just start a new one. Usually the restart is to get new code, so you can start a fresh process without waiting for the old one to end, optionally using the child_process module to have a toplevel script managing the whole thing. Or even use the cluster module, allowing you to start the new process before you've even shut down the old one (since cluster manages balancing traffic between its child instances).

One thing I haven't actually tested very far, is whether it's guaranteed safe to start a new server as soon as server.close() returns. If not, then the new server could potentially fail to bind. There's an example in the server.listen() docs about how to handle such an EADDRINUSE error.

Answer 2

By default there's no socket timeout, that means that connections will be open forever until the client closes them. If you want to set a timeout use this function: socket.setTimeout.

If you try to close the server you simply can't because there are active connections, so if you try to gracefully shutdown the shutdown function will hang up. The only way is to set a timeout and when it expires kill the app.

If you have workers it's not as simple as killing the app with process.exit(), so I made a module that does extacly what you're asking: grace.