Ticket Booking
An on-sale stampede where a queue is the waiting room, not a failure.
Survive the on-sale stampede with a queue as the waiting room — no oversold seats, no melted checkout, even as a checkout node dies.
When tickets go on sale, demand arrives as a wall, not a ramp. No fleet you can afford absorbs the first minute raw — a queue has to buffer the stampede and feed checkout at a rate the inventory store can survive, while a cache serves the seat-map reads everyone hammers while they wait.
Components in play
- Edge LB — Takes the front of the stampede and spreads it across the gateways.
- Sale gateway — Admits fans into the sale; the tier that sees the raw spike first.
- Waiting room — Buffers the on-sale wall and feeds checkout at a survivable rate.
- Checkout service — Holds seats, takes payment, confirms the order.
- Checkout fan-out — Splits checkout output between the inventory write path and the seat-map cache so both carry real traffic.
- Seat-map cache — Serves the seat-map reads everyone refreshes while they wait.
- Inventory store — Source of truth for seats — the thing that must never oversell.
Graded on these SLOs
- ≥ 97.00%Orders succeed
- ≤ 160 msCheckout p99
- ≥ 9.0k rpsSell the house
- ≤ 10Lean footprint
The brief
Design the on-sale path for event tickets: when tickets go live, demand arrives as a wall in the same second, not a ramp. No fleet you can afford absorbs that first second raw, so admission has to be buffered and checkout has to drain it at a rate the seat inventory can survive — no oversold seats, ever.
Functional
- Show the seat map and live availability
- Admit fans into the sale and hold a seat during checkout
- Confirm payment without overselling a seat
Non-functional
- Demand arrives as an instant wall the moment the sale opens
- A seat is never double-sold, even under contention
- Fans in line eventually get an answer, not a dropped connection
Warm-up: design decisions
Optional theory to prime the calls a senior engineer would make before you build.
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