Message Queues with Bull

Background jobs are essential for time-consuming tasks. Bull makes it easy with Redis.

Setup

```bash npm install bull ```

Make sure Redis is running: ```bash redis-server ```

Basic Queue

```javascript const Queue = require('bull');

const emailQueue = new Queue('email', { redis: { host: '127.0.0.1', port: 6379 } });

async function sendWelcomeEmail(userId, email) { await emailQueue.add({ userId, email, type: 'welcome' }); }

emailQueue.process(async (job) => { const { userId, email, type } = job.data; console.log(`Sending ${type} email to ${email}`); await sendEmail(email); return { sent: true }; });

await sendWelcomeEmail(123, 'user@example.com'); ```

**What happens:** 1. Job added to queue 2. Worker picks up job 3. Processes asynchronously 4. Main app continues without waiting

Real Example: Image Processing

```javascript const Queue = require('bull'); const sharp = require('sharp');

const imageQueue = new Queue('image-processing');

app.post('/upload', upload.single('image'), async (req, res) => { await imageQueue.add({ filename: req.file.filename, path: req.file.path }); res.json({ message: 'Processing started' }); });

imageQueue.process(async (job) => { const { path, filename } = job.data; await sharp(path) .resize(800, 600) .toFile(`uploads/resized-${filename}`); await sharp(path) .resize(200, 200) .toFile(`uploads/thumb-${filename}`); return { processed: true }; }); ```

Job Events

```javascript emailQueue.on('completed', (job, result) => { console.log(`Job ${job.id} completed`, result); });

emailQueue.on('failed', (job, err) => { console.error(`Job ${job.id} failed`, err); });

emailQueue.on('progress', (job, progress) => { console.log(`Job ${job.id} is ${progress}% done`); }); ```

Job Options

```javascript await emailQueue.add(data, { attempts: 3, backoff: { type: 'exponential', delay: 2000 } });

await emailQueue.add(data, { delay: 5000 });

await emailQueue.add(data, { priority: 1 });

await emailQueue.add(data, { removeOnComplete: true, removeOnFail: false }); ```

Scheduled Jobs

```javascript await emailQueue.add(data, { repeat: { cron: '0 9 * * *' } });

await emailQueue.add(data, { repeat: { every: 5 * 60 * 1000 } }); ```

Multiple Workers

```javascript imageQueue.process(5, async (job) => { await processImage(job.data); }); ```

Processes 5 jobs concurrently.

Key Takeaway

Bull handles background jobs with Redis. Add jobs to queue, process asynchronously. Automatic retries and scheduling. Perfect for emails, image processing, reports.