Design a fault-tolerant Payment System
Last updated: September 22, 2025
Quick Overview
Design a fault-tolerant payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Snowflake
September 22, 20250
4
1,638 solved
Design a fault-tolerant payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Snowflake 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
- How would you handle a region-wide outage?
- How would you handle schema migrations with zero downtime?
- 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
- Payment Processing: The system must accept payments through various methods (credit card, bank transfer, etc.).
- Transaction History: Users must be able to vie...
Capacity Estimation
Assuming Snowflake expects to handle approximately 10 million transactions per day:
- Transactions per second (TPS): 10M transactions/day / 86400 seconds/day = ~115.74 TPS.
- Peak Load: Assumi...
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