Job Queues

BullMQ (Node.js — recommended)

import { Queue, Worker, QueueEvents } from 'bullmq';
import IORedis from 'ioredis';

const connection = new IORedis(process.env.REDIS_URL);

// Define queue
const emailQueue = new Queue('emails', { connection });

// Add job
await emailQueue.add('send-welcome', {
  userId: '123',
  template: 'welcome',
}, {
  attempts: 3,
  backoff: { type: 'exponential', delay: 2000 },
  removeOnComplete: { age: 24 * 3600 }, // Cleanup after 24h
  removeOnFail: { age: 7 * 24 * 3600 },
});

// Add delayed job
await emailQueue.add('send-reminder', { userId: '123' }, {
  delay: 24 * 60 * 60 * 1000, // 24 hours
});

// Add prioritized job
await emailQueue.add('send-alert', { orderId: '456' }, {
  priority: 1, // Lower number = higher priority
});

Worker

const worker = new Worker('emails', async (job) => {
  switch (job.name) {
    case 'send-welcome':
      await sendWelcomeEmail(job.data.userId, job.data.template);
      break;
    case 'send-reminder':
      await sendReminderEmail(job.data.userId);
      break;
  }

  // Report progress
  await job.updateProgress(50);
  await doMoreWork();
  await job.updateProgress(100);
}, {
  connection,
  concurrency: 5,
  limiter: { max: 10, duration: 1000 }, // Rate limit: 10 jobs/sec
});

worker.on('completed', (job) => console.log(`Job ${job.id} completed`));
worker.on('failed', (job, err) => console.error(`Job ${job?.id} failed:`, err.message));

Celery (Python)

from celery import Celery

app = Celery('tasks', broker='redis://localhost:6379/0')

@app.task(bind=True, max_retries=3, default_retry_delay=60)
def send_email(self, user_id: str, template: str):
    try:
        user = get_user(user_id)
        mailer.send(user.email, template)
    except ConnectionError as exc:
        self.retry(exc=exc)

# Dispatch
send_email.delay('user-123', 'welcome')
send_email.apply_async(args=['user-123', 'welcome'], countdown=3600)  # Delay 1h

# Chain tasks
from celery import chain
workflow = chain(
    process_order.s(order_id),
    send_confirmation.s(),
    update_inventory.s(),
)
workflow.apply_async()

Job Patterns

| Pattern | Use Case | |---------|----------| | Fire-and-forget | Email sending, notifications | | Delayed jobs | Reminders, scheduled tasks | | Job chaining | Multi-step workflows | | Rate-limited | External API calls | | Priority queues | Urgent vs batch processing | | Unique jobs | Prevent duplicate processing |

Monitoring (BullMQ)

const queueEvents = new QueueEvents('emails', { connection });

queueEvents.on('completed', ({ jobId, returnvalue }) => {
  metrics.increment('jobs.completed', { queue: 'emails' });
});

queueEvents.on('failed', ({ jobId, failedReason }) => {
  metrics.increment('jobs.failed', { queue: 'emails' });
});

// Bull Board (dashboard UI)
import { createBullBoard } from '@bull-board/api';
import { BullMQAdapter } from '@bull-board/api/bullMQAdapter';
import { ExpressAdapter } from '@bull-board/express';

const serverAdapter = new ExpressAdapter();
createBullBoard({ queues: [new BullMQAdapter(emailQueue)], serverAdapter });
app.use('/admin/queues', serverAdapter.getRouter());

Anti-Patterns

| Anti-Pattern | Fix | |--------------|-----| | No retry configuration | Set attempts and backoff strategy | | No dead letter handling | Monitor failed jobs, set up alerts | | Processing in request handler | Offload to queue, return 202 Accepted | | No concurrency limits | Set worker concurrency and limiter | | No job cleanup | Configure removeOnComplete and removeOnFail |

Production Checklist

• [ ] Retry with exponential backoff configured
• [ ] Dead letter queue monitoring and alerts
• [ ] Worker concurrency tuned to resource limits
• [ ] Job progress tracking for long-running tasks
• [ ] Dashboard UI for job monitoring (Bull Board)
• [ ] Graceful shutdown: process in-flight jobs before exit