Build a event-driven Ad Serving Pipeline
Last updated: October 21, 2025
Quick Overview
Design a event-driven ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Slack
October 21, 202544
9
2,061 solved
Design a event-driven ad serving system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Slack asks this during the System Design Round 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
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
- What monitoring and alerting would you set up on day one?
- How would you implement rate limiting to protect the system?
- What would the deployment pipeline look like for this system?
- How would you handle a 10x increase in traffic overnight?
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Requirements
Functional Requirements:
- Ad Requests: The system must handle ad requests from various events (e.g., specific channels, user activities) in Slack.
- Ad Personalization: The system shoul...
Capacity Estimation
To estimate capacity:
- Assume Slack has around 10 million active users.
- If every user triggers an ad request 5 times per day, that's 50 million requests daily.
- This translates to approximately 57...
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