How Do I Shut Down My Express Server Gracefully When Its Process Is Killed?

Question

When running my Express application in production, I want to shut down the server gracefully when its process is killed (i.e. a SIGTERM or SIGINT is sent).

Here is a

Answer 1

In case anyone is interested, I found a solution myself (would love to hear feedback in comments).

I added a listener for connections opening on the server, storing references to those connections in an array. When the connections are closed, they are removed from the array.

When the server is killed, each of the connection is closed by calling its end methods. For some browsers (e.g. Chrome), this is not enough, so after a timeout, I call destroy on each connection.

const express = require('express');

const app = express();

app.get('/', (req, res) => res.json({ ping: true }));

const server = app.listen(3000, () => console.log('Running…'));

setInterval(() => server.getConnections(
    (err, connections) => console.log(`${connections} connections currently open`)
), 1000);

process.on('SIGTERM', shutDown);
process.on('SIGINT', shutDown);

let connections = [];

server.on('connection', connection => {
    connections.push(connection);
    connection.on('close', () => connections = connections.filter(curr => curr !== connection));
});

function shutDown() {
    console.log('Received kill signal, shutting down gracefully');
    server.close(() => {
        console.log('Closed out remaining connections');
        process.exit(0);
    });

    setTimeout(() => {
        console.error('Could not close connections in time, forcefully shutting down');
        process.exit(1);
    }, 10000);

    connections.forEach(curr => curr.end());
    setTimeout(() => connections.forEach(curr => curr.destroy()), 5000);
}