Design a large-scale Ad Serving Platform
Last updated: October 22, 2025
Quick Overview
Design a multi-tenant ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Apple
October 22, 202548
3
3,234 solved
Design a multi-tenant ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during System Design Round at Apple. The interviewer expects you to demonstrate your ability to design large-scale distributed systems, make well-reasoned trade-offs, and communicate your thought process clearly. Apple values engineers who can think about scalability from day one.
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 handle a 10x increase in traffic overnight?
- How do you ensure data consistency across multiple services?
- How would you handle schema migrations with zero downtime?
- How would you migrate from a monolithic to a microservices architecture?
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Requirements
Functional Requirements
- Multi-tenant architecture: Support multiple advertisers and ad campaigns with isolation between tenants.
- Ad targeting: Provide real-time targeting based on user d...
Capacity Estimation
To estimate capacity, we analyze the expected scale of the ad serving platform:
- Daily Active Users (DAU): Assume 500 million DAU across platforms (iOS, macOS, etc.).
- Ad Requests per User:...
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