ExpressJS Under Pressure

Monitor your server's health and automatically respond with a "Server Under Pressure" message when certain thresholds are exceeded. This is useful for maintaining server stability under heavy load.

This is an Express JS alternative for @fastify/under-pressure. I will try to add all APIs provided in the fastify plugin in this.

Note: This package is heavily inspired from @fastify/under-pressure. Shoutout to the maintainers and collaborators of the project.

Features

• Monitors event loop delay
• Monitors heap memory usage
• Monitors event loop utilization
• Monitors resident set size (RSS) memory usage
• Configurable thresholds for all metrics
• Customizable response message

Installation

You can install the package using npm:

npm install express-under-pressure

or using yarn:

yarn add express-under-pressure

Usage

Here's a detailed example of how to use the underPressure in an Express application.

Import

First, import the necessary modules in your TypeScript file:

import express from 'express';
import { underPressure } from 'express-under-pressure';

Register the middleware

Next, create an instance of the middleware with your desired options:

const app = express();

underPressure(app, {
  maxEventLoopDelay: 1000, // Maximum event loop delay in milliseconds
  maxHeapUsedBytes: 200 * 1024 * 1024, // Maximum heap used in bytes
  maxRssBytes: 300 * 1024 * 1024, // Maximum RSS memory used in bytes
  maxEventLoopUtilization: 0.98 // Maximum event loop utilisation
  message: 'Server Under Pressure', // Custom response message
});

app.get('/', (req, res) => {
  if (res.locals.isUnderPressure()) {
    // Avoind heavy computations here
  }
  res.send('Hello World!');
});

app.listen(3000, () => {
  console.log('Server is running on port 3000');
});

Middleware Options

The underPressure function takes express app instance and an options object with the following properties:

• maxEventLoopDelay (number): The maximum event loop delay in milliseconds.
• maxHeapUsedBytes (number): The maximum heap memory usage in bytes.
• maxRssBytes (number): The maximum RSS memory usage in bytes.
• maxEventLoopUtilization (number): The maximum event loop utilisation.
• message (string): Optional. The message to send when the server is under pressure.
• retryAfter (number): Optional. The value for Retry-After header..

Contributing

Contributions are welcome! Please open an issue or submit a pull request on GitHub.

License

This project is licensed under the MIT License. See the LICENSE file for details.

Feel free to reach out if you have any questions or need further assistance.

Happy coding!