Request ID for tracing in Express

Introduction

Request ID helps track each request uniquely. It makes debugging and monitoring easier by following a request through the system.

When you want to find problems in logs related to a specific user request.

When multiple requests happen at the same time and you need to separate their logs.

When you want to measure how long a request takes across different parts of your app.

When you want to add tracing information for distributed systems.

When you want to improve support by quickly identifying user actions.

Syntax

Express

app.use((req, res, next) => {
  req.id = generateUniqueId();
  next();
});

This middleware adds a unique ID to each request object.

You can use libraries like uuid to generate unique IDs.

Examples

This example uses the popular uuid library to create a unique request ID.

Express

import { v4 as uuidv4 } from 'uuid';

app.use((req, res, next) => {
  req.id = uuidv4();
  next();
});

This simple example uses the current timestamp as a request ID, which is less unique but easy to implement.

Express

app.use((req, res, next) => {
  req.id = Date.now().toString();
  next();
});

This example generates a short random string as a request ID.

Express

app.use((req, res, next) => {
  req.id = Math.random().toString(36).substring(2, 10);
  next();
});

Sample Program

This Express app adds a unique request ID to every incoming request using the uuid library. It logs the request ID with method and URL, then sends the ID back in the response.

Express

import express from 'express';
import { v4 as uuidv4 } from 'uuid';

const app = express();

// Middleware to add request ID
app.use((req, res, next) => {
  req.id = uuidv4();
  console.log(`Request ID: ${req.id} - ${req.method} ${req.url}`);
  next();
});

app.get('/', (req, res) => {
  res.send(`Hello! Your request ID is ${req.id}`);
});

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

Important Notes

Always generate request IDs early in the middleware chain to track all later actions.

Use a reliable unique ID generator like uuid to avoid collisions.

Include the request ID in logs and responses to help with tracing.

Summary

Request ID uniquely identifies each request for easier tracking.

Add request ID in middleware using libraries like uuid.

Use request ID in logs and responses to improve debugging and monitoring.