Question bank, System design, Most-asked system design
Design an ad click aggregator
Design a system that counts ad clicks per ad per minute for billing and dashboards.
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 10K clicks per second, 2M ads, results within one minute.
- 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. Billing needs exact counts: how do you avoid double counting and recover from failures?
- 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
- Exactly-once counting20 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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