Design a Payment Service
Last updated: April 29, 2026
Quick Overview
Design a scalable payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Confluent
April 29, 202637
7
1,368 solved
Design a scalable payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Confluent 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
- 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 would the deployment pipeline look like for this system?
- How would you handle a 10x increase in traffic overnight?
- How would you handle a region-wide outage?
- How would you migrate from a monolithic to a microservices architecture?
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Requirements
Functional Requirements
- Payment Processing: Ability to process credit/debit card payments, bank transfers, and digital wallets.
- Transaction History: Users must be able to view their ...
Capacity Estimation
Assuming Confluent's payment system needs to handle:
- 1 million transactions per day (Average),
- Peak load of 10,000 transactions per second (TPS).
Back-of-Envelope Calculation
- **Dai...
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