Design a Ad Serving Service
Last updated: March 24, 2026
Quick Overview
Design a real-time ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Robinhood
March 24, 2026147
5
2,675 solved
Design a real-time ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This fundamentals question from Robinhood's System Design Round tests whether you can reason about software design at a deep level. The interviewer expects discussion of maintainability, testability, and operational considerations.
What the Interviewer Expects
- Explain the concept clearly with a practical example
- Discuss when and why to apply this principle
- Identify common mistakes and anti-patterns
- Compare with alternative approaches
Key Topics to Cover
How to Approach This
- Apply SOLID principles. Single Responsibility makes code testable, Open/Closed makes it extensible.
- Choose data structures based on access patterns, not familiarity.
- Prefer immutable data and message passing over shared mutable state for concurrency.
- Design APIs with RESTful conventions, versioning, meaningful errors, and pagination from day one.
Possible Follow-up Questions
- What testing strategy would you use for this component?
- How would you handle backward compatibility?
- How would you document this for other engineers?
- How would this design change if the team size doubled?
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Core Design Principles
For the ad serving service, the following core design principles apply:
- SOLID Principles: Particularly, the Single Responsibility Principle is crucial. Each component of the system (ad sel...
Architecture
The architecture for the ad serving service will follow a microservices model. This will consist of several key components:
- API Gateway: This handles incoming requests, routes them to appr...
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