Message Queues with Bull

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

Setup

npm install bull

Make sure Redis is running:

redis-server

Basic Queue

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

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

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

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

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

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

Multiple Workers

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.