Design Payment Infrastructure for microservices
Last updated: February 4, 2026
Quick Overview
Design a event-driven payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Compass
February 4, 20266
4
2,942 solved
Design a event-driven payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Compass typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
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 region-wide outage?
- How would you optimize costs as the system scales?
- What happens if one of your database nodes goes down?
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Requirements
Functional Requirements
- Payment Processing: The system must process payments in real-time for various services offered by Compass.
- Event-Driven Architecture: Payments should trigger ...
Capacity Estimation
Assuming Compass handles 10 million users and each user makes an average of 2 transactions per day:
- Total Transactions per Day: 10 million users * 2 transactions = 20 million transactions/day. ...
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