Design a Real-Time Notification System with Fan-Out
Last updated: March 3, 2025
Quick Overview
One creator posts and millions of followers get push notifications. Design fan-out strategies, message queuing, device management, and delivery guarantees.
ByteDance
System Design
Software Engineer
ByteDance
March 3, 2025Software Engineer
System Design Round
System Design
Hard
6
6
3,217 solved
One creator posts and millions of followers get push notifications. Design fan-out strategies, message queuing, device management, and delivery guarantees.
Tests distributed systems fundamentals at TikTok scale where a single creator action triggers millions of downstream events.
What the Interviewer Expects
- Compare push versus pull versus hybrid fan-out strategies
- Design message queuing with Kafka for durability
- Implement device token management for push notifications
- Address deduplication and rate limiting per user
- Discuss at-least-once versus exactly-once delivery
Key Topics to Cover
Fan-out patterns
Message queuing
Push notifications
Deduplication
Delivery guarantees
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 do you handle creators with 100M+ followers?
- What is your strategy for notification fatigue?
- How do you ensure notifications arrive within seconds?
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Practice System Design ProblemsSample Answer
Requirements
- Functional Requirements:
- Users (followers) should receive real-time push notifications when a creator posts new content.
- The system must support deduplication of notifications to avoid f...
Capacity Estimation
- Estimating Scale:
- Assuming TikTok has around 1 billion users, let's estimate 10% are active at any given moment, resulting in 100 million active users.
- If a creator posts content, let’s ...
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