Add a Graceful Shutdown Handler

1. Track a shuttingDown flag and make readiness return 503 as soon as termination starts.

let shuttingDown = false;

app.get('/readyz', (_req, res) => {
  res.status(shuttingDown ? 503 : 200).json({ ready: !shuttingDown });
});

Expected output: Once shutdown begins, readiness returns 503 and the load balancer removes the instance.

2. Stop accepting connections, close idle keep-alive sockets, and wait for active requests before exiting.

const server = app.listen(3000);

function shutdown(signal) {
  if (shuttingDown) return;
  shuttingDown = true;
  console.log(JSON.stringify({ event: 'shutdown', signal }));

  server.close((error) => {
    if (error) {
      console.error(error);
      process.exitCode = 1;
    }
    process.exit();
  });
  server.closeIdleConnections();

  setTimeout(() => {
    console.error('drain deadline exceeded');
    process.exit(1);
  }, 15_000).unref();
}

process.on('SIGTERM', () => shutdown('SIGTERM'));
process.on('SIGINT', () => shutdown('SIGINT'));

Expected output: In-flight requests finish; the process exits 0 after they complete or 1 after the drain deadline.

3. Send SIGTERM during a slow request and confirm the request completes while a new request is refused or redirected.

kill -TERM <pid>

Expected output: The slow request receives a complete response and the process exits within the drain window.

Problem

The process waits forever

Solution

Keep-alive connections are still open. Call server.closeIdleConnections and enforce a hard deadline.

Problem

New requests still arrive during shutdown

Solution

Readiness must fail before draining, and the load balancer needs time to observe it.