Queues, workers, and event-driven architecture
By the end of today you can decide what work belongs outside the request, explain what a queue guarantees and what it does not, and say why every consumer must tolerate seeing the same message twice.
YesterdayOn Day 17 a queue was a data structure. On Day 55 you learned retries and idempotency keys. Today those combine across machines.
TomorrowTomorrow, the opposite problem: pushing data to users the moment it changes.
Why this matters
Queues are how systems stay responsive under load and survive dependencies being down. They also introduce duplicate delivery and ordering problems that surprise people who expected a simple pipe.
- Message queues
- Background workers
- Delivery guarantees
- Event-driven architecture
Learn it
80 minCopy this into Claude or ChatGPT. It quizzes you before it explains anything, which is deliberate. The resources under it are how you check what it told you.
Today's Master Prompt
Free · sign inA prompt written for this day alone: your level, the exact scope, what to leave out, and an instruction to quiz you before it explains anything. Paste it into Claude or ChatGPT and it teaches you today's material.
Check it against something that is not a model
An assistant can be fluent and wrong, and on a topic you met today you will not catch it. These cover the same ground and were made by people who do this for a living, so they are what you hold the explanation up against. They are other people's work and we only link to them, so judge them for yourself.
3 hand-picked resources
Free · sign inVideos, official docs and articles covering the same ground, each opened and annotated by hand. They are what you check the assistant against on a day you cannot yet catch it being wrong.
Build it
50 minMove one slow operation out of a request into a queue with a worker. Confirm the endpoint returns immediately and the work still happens. Then deliberately deliver the same message twice and observe the damage. Make the consumer idempotent and confirm the duplicate is now harmless. Finally, stop the worker and watch queue depth grow.
Recall it
20 minAnswer out loud, reveal, then mark honestly whether you had it. That score is the only thing on this page you do not get to choose.
5 recall questions
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Rate it
Completion and mastery are tracked separately. Be honest, because an inflated rating only means the concept resurfaces sooner.
Mastery tracking
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Recap
- 01A queue trades immediate feedback for responsiveness and resilience
- 02At-least-once is the norm, so duplicates are normal operation
- 03Exactly-once effects come from idempotent consumers, not from the broker
- 04Queue depth tells you whether you are keeping up, long before anything breaks
Your progress
Free · sign inMark days complete, pick up where you left off across devices, and watch completion and mastery diverge. Free, and the account exists only so ninety days of work cannot vanish with a cleared browser.