Event-Driven Background Jobs¶
Trigger work in response to something happening, not on a fixed schedule. A file lands in storage, an order is placed, a message arrives — and a handler runs. The most common shape for background work in a modern distributed system.
flowchart LR
Junior["Junior: trigger vs. schedule, the basic event-handler shape"] --> Middle["Middle: at-least-once delivery and handler idempotency"]
Middle --> Senior["Senior: ordering, backpressure, poison messages"]
Senior --> Professional["Professional: event-driven job systems at scale"]
flowchart LR
Event["Event occurs\n(file uploaded, order placed)"] --> Queue["Message queue /\nevent bus"]
Queue --> Handler["Background job handler\n(consumes and processes)"]
Handler --> Result["Side effect: email sent,\nrecord updated, etc."]
Choose a level¶
| Level | Guide | You are done when |
|---|---|---|
| Junior | Trigger vs. schedule | You can explain when event-driven jobs are the right shape versus a fixed schedule. |
| Middle | At-least-once delivery | You can explain why a handler might run twice for one event, and what that requires of your handler. |
| Senior | Ordering and poison messages | You can explain what happens when one bad message blocks a queue, and how ordering guarantees interact with parallelism. |
| Professional | Event-driven systems at scale | You can design a production event-driven job system's failure handling, backpressure, and observability. |
Practice rule¶
For any event-driven handler you write, ask: "if this exact event were delivered twice, in a row, right now — what happens?" If the answer isn't "nothing bad," the handler isn't safe for at-least-once delivery, which is what almost every real message queue provides.