Design a fault-tolerant Messaging System
Last updated: November 30, 2025
Quick Overview
Design a fault-tolerant messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Stripe
System Design
Software Engineer
Stripe
November 30, 2025Software Engineer
Onsite
System Design
Medium
88
12
3,354 solved
Design a fault-tolerant messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Stripe 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
- 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
Database selection and data modeling
Consistency models and replication
Partitioning and sharding strategies
High-level architecture and component design
Message queues and async processing
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 would you optimize costs as the system scales?
- How would you handle a region-wide outage?
- How would you implement rate limiting to protect the system?
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Requirements
- Functional Requirements:
- Ability to send messages between users in real-time.
- Support for both synchronous and asynchronous messaging.
- User presence indicators (online/offli...
Capacity Estimation
- User Base:
Assume 100 million active users. - Message Volume:
- Assume an average user sends 2 messages per minute.
- Thus, total messages per minute = 100 million users * 2 ...
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