Graceful Shutdown

A graceful shutdown is the process of stopping a Node.js application while ensuring that all currently active requests are completed, database connections are closed, and other resources are released properly.

Why is it important?

Data Integrity: Ensures database operations aren’t interrupted mid-way.
User Experience: Allows current users to finish their requests.
Reliability: Reduces “zombie” processes or leaked resources in production environments like Docker or Kubernetes.

Step-by-Step Implementation

1. Identify Termination Signals

Listen for SIGTERM (sent by orchestrators) and SIGINT (Ctrl+C).

2. Implementation Example

Here’s how you can implement a graceful shutdown in an Express app:

const express = require('express');
const app = express();
const server = app.listen(3000);

// Example DB connection
const db = require('./db');

process.on('SIGTERM', () => {
  console.info('SIGTERM signal received.');

  console.log('Closing http server.');
  server.close(() => {
    console.log('Http server closed.');

    // Close DB connections
    db.close(() => {
    console.log('Database connection closed.');
    process.exit(0);
    });
  });

  // If server hasn't finished in 10s, force shutdown
  setTimeout(() => {
    console.error('Could not close connections in time, forcefully shutting down');
    process.exit(1);
  }, 10000);
});

Production Tips

Timeouts: Always set a timeout (e.g., 10-30 seconds) to force quit if the cleanup takes too long.
Process Managers: PM2 and Kubernetes handle these signals gracefully if your code is prepared for them.

[!TIP] Use the stoppable npm package if you want more robust control over closing existing connections in your HTTP server.