System Design - lesson 5 | HackIndia Skills

System Design - lesson 5 | HackIndia Skills | HackIndia

Example

Node queue example

This uses BullMQ with Redis. Redis is the broker here. Your API adds the job. A separate worker file processes it.

Install with npm install bullmq ioredis. Run Redis locally with Docker if you already use Docker.

// queue.js
const { Queue } = require('bullmq');

const connection = { host: '127.0.0.1', port: 6379 };

const emailQueue = new Queue('email', {
  connection,
  defaultJobOptions: {
    attempts: 3,
    backoff: { type: 'exponential', delay: 5000 },
    removeOnComplete: true,
    removeOnFail: false
  }
});

module.exports = { emailQueue };

// api.js
const express = require('express');
const { emailQueue } = require('./queue');
const app = express();
app.use(express.json());

app.post('/orders', async (req, res) => {
  const orderId = 'ord_' + Date.now();

  // Save order to DB here first
  await emailQueue.add('send-order-confirmation', {
    orderId,
    email: req.body.email
  });

  res.status(202).json({ orderId, status: 'queued' });
});

app.listen(3000);

// worker.js
const { Worker } = require('bullmq');

const connection = { host: '127.0.0.1', port: 6379 };

new Worker('email', async (job) => {
  console.log('Sending email for', job.data.orderId);
  // Call email provider here
  // Update order notification_status in DB
}, { connection });

Use queues for slow work

Remember this

When to use it

Basic flow

Node queue example

Avoid this mistake

Keep jobs small

What to document

Do this now

Quick check