Bull / BullMQ Job Queues with Redis
A job queue decouples time-consuming background work from HTTP request handling. Instead of performing the work synchronously — sending emails, processing images, generating PDFs, calling slow third-party APIs — a route handler adds a job to a queue and returns immediately. A separate worker process consumes the job and performs the work asynchronously. Bull and BullMQ are the two most popular Redis-backed job queue libraries for Node.js; BullMQ is the modern rewrite with better TypeScript support and a cleaner API.
Analogy🏏Cricket
Think of it like cricket: The team selection committee doesn't debate each player's fitness report while the player stands in the lobby. The physio submits a report (adds a job to the queue), the player is free to leave (HTTP response returns), and the committee reviews it in their scheduled meeting room (worker process). If the committee is busy, reports stack up in their inbox (Redis queue) and are processed in order. Jasprit Bumrah's fitness report goes in the queue; the selectors process it when they're ready.