Design a Ad Serving Service
Last updated: May 6, 2026
Quick Overview
Design a distributed ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Dropbox
May 6, 2026321
14
2,932 solved
Design a distributed ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Dropbox typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
What the Interviewer Expects
- Systematically gather requirements and estimate capacity (QPS, storage, bandwidth)
- Design a scalable architecture with clear component responsibilities
- Make well-reasoned database and caching decisions with trade-off analysis
- Address consistency vs availability trade-offs specific to the use case
- Discuss partitioning strategy, replication, and data modeling
- Cover failure handling, monitoring, and alerting strategies
Key Topics to Cover
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you optimize costs as the system scales?
- How would you migrate from a monolithic to a microservices architecture?
- How would you implement rate limiting to protect the system?
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Requirements
Functional Requirements:
- Ad Inventory Management: Ability to manage a catalog of ads, including details like ad content, targeting criteria, and pricing.
- Ad Serving: Serve relevant a...
Capacity Estimation
To estimate capacity, we need to consider:
- User Base: Assume Dropbox has 500 million active users.
- Ad Requests: If we assume each user generates 10 ad requests per day, that translates to:...
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