Question bank, System design, Top system design
Design a payment system
Design the payment backend for an e-commerce site using an external payment processor.
45 minutes, for mid-level, senior engineers
How the interview runs
- 1.Requirements. Before we design anything: what are the core functional requirements, and which non-functional ones matter most here?
- 2.Estimates. Let's size it. Assume 1M orders a day with spikes on sale days.
- 3.API + data model. What does the API look like, and how would you model and store the data?
- 4.High-level design. Walk me through the high-level architecture, request by request.
- 5.Deep dive. How do you make sure a customer is never charged twice and the books always balance?
- 6.Trade-offs + failure. What are the main trade-offs you made, and what happens when a component fails?
What you're graded on
- Clarified requirements15 pts
- Back-of-envelope estimates10 pts
- Clear API10 pts
- Data model + storage choice15 pts
- Coherent architecture15 pts
- Idempotency + reconciliation20 pts
- Trade-offs8 pts
- Failure handling7 pts
Practice this one for real
Answer it phase by phase, then get the rubric score, what you missed and the model answer outline.
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