Design a scalable Ad Serving System
Last updated: October 7, 2025
Quick Overview
Design a scalable ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Netflix
System Design
Software Engineer
Netflix
October 7, 2025Software Engineer
Onsite
System Design
Easy
10
3
2,791 solved
Design a scalable ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Netflix asks this during the Onsite to assess your architectural thinking. They want to see how you decompose a complex problem, choose appropriate technologies, and reason about failure modes. Strong candidates proactively discuss monitoring, alerting, and operational concerns.
What the Interviewer Expects
- Clearly define functional and non-functional requirements
- Propose a reasonable high-level architecture with core components
- Choose appropriate data storage solutions with basic justification
- Discuss basic scaling strategies (horizontal scaling, caching)
- Identify potential bottlenecks and suggest simple solutions
Key Topics to Cover
Partitioning and sharding strategies
Consistency models and replication
API design and rate limiting
Requirements gathering and capacity estimation
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 implement rate limiting to protect the system?
- What would the deployment pipeline look like for this system?
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Requirements
Functional Requirements:
- Ad Request Handling: The system must serve ads based on user profiles, preferences, and viewing history.
- Ad Inventory Management: Ability to manage various a...
Capacity Estimation
To estimate capacity, let’s assume:
- Daily Active Users (DAUs): 200 million
- Ad Requests per User: 3 requests per session
- Sessions per User: 1 session per day
Calculations:
- Tot...
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