Week 5 Day 5: Mini Project - Job Queue with BullMQ

We will build an Email Sending System. Since SMTP servers are slow, we will offload the sending to a Background Worker.

Requirements

Redis Installed.
bullmq library.

1. Setup

npm install express bullmq ioredis

2. The Producer (`producer.js`)

This is the API server.

const express = require('express');
const { Queue } = require('bullmq');

const app = express();
app.use(express.json());

// Connection to Redis
const connection = { host: '127.0.0.1', port: 6379 };

// Create Queue
const emailQueue = new Queue('email-queue', { connection });

app.post('/send-email', async (req, res) => {
    const { to, subject, body } = req.body;
    
    // Add Job to Queue
    await emailQueue.add('send-email-job', { to, subject, body });

    res.json({ status: 'Queued', message: 'Email will be sent shortly.' });
});

app.listen(3000, () => console.log('API running on 3000'));

3. The Worker (`worker.js`)

This runs in the background.

const { Worker } = require('bullmq');

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

// Simulate sending email (2 seconds delay)
const sendEmail = async (job) => {
    console.log(`Processing Job ${job.id}: Sending email to ${job.data.to}...`);
    await new Promise(r => setTimeout(r, 2000));
    console.log(`Job ${job.id} Done! Email Sent.`);
};

const worker = new Worker('email-queue', async (job) => {
    await sendEmail(job);
}, { connection });

console.log('Worker listening for jobs...');

4. Run it

Start Redis.
Run node worker.js (Worker acts as consumer).
Run node producer.js.
POST a request.
- API returns “Queued” instantly (10ms).
- Worker logs “Processing…” and finishes 2s later.

Congratulations! You decoupled your API from the heavy task. 🦅 Next week: Microservices. Breaking the Monolith! 🔨

Next Step

Next: Monolith Vs Microservices →