Compression

Compression reduces the size of the HTTP response body before it is sent over the network, drastically decreasing bandwidth usage and improving perceived load times for clients.

Overview

When an API returns a massive JSON payload (e.g., 5MB of analytics data), transferring that data over a 3G mobile connection could take several seconds.

By enabling gzip or Brotli compression, that 5MB JSON string can often be compressed down to 500KB (a 90% reduction), significantly speeding up the transfer. The client’s browser or HTTP library automatically decompresses it upon receipt.

Key Concepts

• Gzip: The historical standard for HTTP compression. Fast and universally supported by all clients.
• Brotli (br): A newer compression algorithm developed by Google. It offers significantly better compression ratios than Gzip, especially for text (JSON/HTML), but uses slightly more CPU to compress.
• Trade-off (CPU vs Network): Compression trades CPU cycles for network bandwidth. It takes CPU power to compress the JSON string.

Code Examples

1. Enabling Compression in NestJS

NestJS provides an easy wrapper via the compression middleware package.

npm install compression
npm install @types/compression -D

Enable it in your main.ts file:

// main.ts
import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import * as compression from 'compression';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  
  // Enable gzip compression for all routes
  app.use(compression());
  
  await app.listen(3000);
}
bootstrap();

2. Advanced Configuration

By default, the compression middleware uses Gzip. You can configure the threshold (don’t compress tiny payloads, as the CPU cost isn’t worth the microscopic network savings) and filter which requests get compressed.

app.use(compression({
  // Only compress responses larger than 1024 bytes (1KB)
  threshold: 1024,
  
  // Custom filter logic
  filter: (req, res) => {
    if (req.headers['x-no-compression']) {
      // Don't compress responses if this specific header is present
      return false;
    }
    // Fallback to standard compression filter (compresses standard text/json types)
    return compression.filter(req, res);
  }
}));

Best Practices

• Offload Compression to the Reverse Proxy (Recommended): While doing compression inside Node.js is easy, Node.js is single-threaded. Compressing a 10MB JSON payload will block the event loop, causing latency spikes for all other users. For high-performance systems, do not enable compression in NestJS. Instead, place an Nginx reverse proxy or an AWS Application Load Balancer (ALB) in front of your Node app and let them handle the compression. They are written in C/C++ and handle compression much more efficiently than Node.js.
• Don’t Compress Everything: Never compress images (JPEG, PNG, WebP) or videos (MP4). They are already highly compressed formats. Attempting to gzip a JPEG will waste CPU and might actually increase the file size. Only compress text-based formats (JSON, XML, HTML, CSS, JS).