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Add the operations your service exposes. Method, path, and status codes make your API much easier to review.
Policies that aren't specific to a single endpoint — auth, rate limits, versioning, and other notes.
Diagram
Draw the components and how traffic flows between them. Notes below the canvas are optional — the Walkthrough panel is the primary place to narrate flows.
Request walkthrough
Trace each core requirement as an ordered sequence of hops through your diagram. Use component names from your canvas for the From / To columns.
Users can browse events and view available seats on a venue map.
Users can select 1-6 seats and proceed to checkout.
Selected seats are temporarily held (locked) for the user during checkout (e.g. 10 minutes).
After successful payment, seats are confirmed and a booking is created.
No seat can be sold to two different users (no double-booking).
Storage schema
For each entity, declare how it's stored. Sharding key is the interesting one — pick the access pattern it optimises for.
A concert, sports match, or show at a specific venue, date, and time.
A specific seat in a venue with section, row, number. States: available → held → booked.
A temporary lock on 1-6 seats for a user, with a TTL (e.g. 10 min). Expires if payment is not completed.
A confirmed reservation: user + seats + payment reference. Immutable after creation.
Component choices
Pick one per row and give a one-line reason. These are the concrete technology decisions your diagram implies.
How traffic is distributed to your app servers.
Where hot reads are served from.
Primary durable store for entities.
Async work buffer for writes/fan-out.
Your diagram
No components drawn yet — edit the diagram before answering.
Iterate on your design — don't start over.
Each scenario below probes a specific weakness in a typical HLD. Reference components from your diagram by name, describe what breaks and at what load, then name the minimum change that fixes it. Strong answers identify the precise failure mode — not just "scale it up".
A scalper bot holds 500 seats across 50 browser sessions, waits 9 minutes, then buys them all. How do you prevent this?
Probes: abuse rate limiting