--- name: job-queue-502199fe97b0 description: >- Build job queues and background worker systems using BullMQ, Celery, or Sidekiq. Use when you need to offload slow tasks from request handlers — email sending, PDF generation, image processing, data exports, or any work that takes more than a few hundred milliseconds. Covers job priorities, concurrency control, scheduled jobs, progress tracking, and graceful shutdown. Trigger words: background job, worker, queue, async task, BullMQ, Celery, cron job, scheduled task, job retry. license: Apache-2.0 compatibility: "BullMQ 6 needs Redis 6.2+ (Sidekiq: Redis; Celery: RabbitMQ or Redis). Node.js 18+ or Python 3.10+." metadata: author: terminal-skills version: "1.1.0" category: development tags: "job-queue, background-workers, async, BullMQ" repository: "https://github.com/taskforcesh/bullmq" --- # Job Queue ## Overview This skill helps you build production-grade background job processing systems. It covers queue architecture, worker concurrency, job priorities, retry strategies, scheduled/recurring jobs, progress reporting, and graceful shutdown. The patterns work across BullMQ (Node.js), Celery (Python), and Sidekiq (Ruby). ## Instructions ### 1. Set up the queue and define job types Create typed job definitions and a queue instance: ```typescript // src/jobs/types.ts export interface JobMap { "email:send": { to: string; template: string; data: Record }; "pdf:generate": { reportId: string; format: "a4" | "letter" }; "export:csv": { userId: string; query: string; columns: string[] }; "image:resize": { sourceUrl: string; widths: number[] }; } // src/jobs/queues.ts import { Queue } from "bullmq"; import { JobMap } from "./types"; const connection = { host: "localhost", port: 6379 }; // BullMQ keeps finished jobs in Redis by default; cap them here or memory grows forever. const defaultJobOptions = { removeOnComplete: { age: 24 * 3600, count: 1000 }, // seconds / count removeOnFail: { age: 7 * 24 * 3600 }, }; export const emailQueue = new Queue("email", { connection, defaultJobOptions }); export const pdfQueue = new Queue("pdf", { connection, defaultJobOptions }); export const exportQueue = new Queue("export", { connection, defaultJobOptions }); export const imageQueue = new Queue("image", { connection, defaultJobOptions }); ``` ### 2. Implement workers with concurrency control ```typescript // src/workers/email-worker.ts import { Worker, Job } from "bullmq"; import { JobMap } from "../jobs/types"; const emailWorker = new Worker( "email", async (job: Job) => { const { to, template, data } = job.data; await job.updateProgress(10); const html = await renderTemplate(template, data); await job.updateProgress(50); await sendEmail(to, html); await job.updateProgress(100); return { sentAt: new Date().toISOString() }; }, { connection: { host: "localhost", port: 6379 }, concurrency: 10, // Process 10 emails in parallel limiter: { max: 100, duration: 60000 }, // Rate limit: 100/minute } ); emailWorker.on("completed", (job) => { console.log(`Email sent: job ${job.id} → ${job.data.to}`); }); emailWorker.on("failed", (job, err) => { console.error(`Email failed: job ${job?.id} — ${err.message}`); }); ``` ### 3. Add job scheduling and priorities ```typescript // Delayed job — send welcome email 30 minutes after signup await emailQueue.add("email:send", { to: "jun.park@northwind.io", template: "welcome", data: { name: "Alex" }, }, { delay: 30 * 60 * 1000 }); // Priority jobs — password resets jump the queue await emailQueue.add("email:send", { to: "maria.lopez@northwind.io", template: "password-reset", data: { resetLink: "https://app.northwind.io/reset/7f3c9e2a" }, }, { priority: 1 }); // Lower number = higher priority // Recurring job — daily digest at 8:00 AM UTC, as a Job Scheduler. // BullMQ 6 removed queue.add(..., { repeat }); upsertJobScheduler replaces it. // Calling it again with the same ID updates the schedule instead of adding a duplicate. await emailQueue.upsertJobScheduler( "daily-digest", { pattern: "0 8 * * *", tz: "UTC" }, { name: "email:send", data: { to: "digest", template: "daily-digest", data: {} }, opts: { attempts: 3, removeOnFail: 1000 }, } ); // Remove the schedule when the feature is retired await emailQueue.removeJobScheduler("daily-digest"); ``` Each run produces a normal job, so retries, priorities and removal rules apply. You cannot set a custom `jobId` on the jobs a scheduler creates. ### 4. Implement graceful shutdown ```typescript // src/workers/shutdown.ts const workers = [emailWorker, pdfWorker, exportWorker, imageWorker]; async function gracefulShutdown(signal: string): Promise { console.log(`Received ${signal}. Closing workers gracefully...`); await Promise.all(workers.map((w) => w.close())); console.log("All workers closed. Exiting."); process.exit(0); } process.on("SIGTERM", () => gracefulShutdown("SIGTERM")); process.on("SIGINT", () => gracefulShutdown("SIGINT")); ``` ## Examples ### Example 1: PDF report generation queue **Prompt:** "Build a background job system for generating PDF reports. Users request a report, get a job ID back immediately, and can poll for progress. Reports take 10-30 seconds to generate." **Agent output:** - Creates `src/jobs/pdf-queue.ts` with typed job definitions - Creates `src/workers/pdf-worker.ts` with progress updates at each stage (query data → format → render → upload) - Creates `src/routes/reports.ts` with `POST /reports` (enqueue, return job ID) and `GET /reports/:jobId/status` (return progress percentage and download URL when complete) - Adds retry logic: 3 attempts with 10-second backoff ### Example 2: Image processing pipeline **Prompt:** "I need to process uploaded images: resize to 3 widths (200, 800, 1600px), convert to WebP, and upload to cloud storage. Handle up to 500 images per hour." **Agent output:** - Creates `src/workers/image-worker.ts` with sharp-based resize and conversion pipeline - Sets concurrency to 4 (CPU-bound work, matches core count) - Adds per-image progress tracking (useful for batch uploads) - Creates `src/jobs/image-pipeline.ts` with a flow: resize → convert → upload as chained jobs ## Guidelines - **Keep jobs serializable** — job data must survive JSON round-trips. Pass IDs and URLs, not buffers or streams. - **Set appropriate concurrency** — CPU-bound work (image processing): match core count. I/O-bound (email, API calls): 10-50 concurrent. - **Always implement graceful shutdown** — `SIGTERM` should let running jobs finish before the process exits. `worker.close()` stops taking new jobs and waits for active ones, with no timeout of its own, so keep job runtimes bounded. Workers default to `concurrency: 1`; set it explicitly as above. - **Use job IDs for idempotency** — set a deterministic `jobId` to prevent the same job from being enqueued twice. - **Monitor queue depth** — a growing queue means workers can't keep up. Alert when backlog exceeds 5 minutes of processing time. - **Separate queues by workload type** — don't let a slow PDF generation block fast email sends. - **Store results externally** — finished jobs are kept in Redis by default, but `removeOnComplete` and `removeOnFail` trim them (see the queue setup above). 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