Design Payment Infrastructure for global users
Last updated: May 20, 2026
Quick Overview
Design a real-time payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
HRT
System Design
Software Engineer
HRT
May 20, 2026Software Engineer
Onsite
System Design
Hard
20
13
4,403 solved
Design a real-time payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
HRT 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
- Drive the design discussion proactively with minimal interviewer guidance
- Perform detailed capacity estimation and use it to inform design decisions
- Design for global scale with multi-region deployment and data consistency
- Deep dive into 2-3 critical components with implementation-level detail
- Address complex trade-offs: CAP theorem, eventual consistency, conflict resolution
- Discuss operational excellence: deployment strategy, chaos engineering, SLOs/SLIs
- Propose a phased rollout plan from MVP to full-scale system
Key Topics to Cover
API design and rate limiting
High-level architecture and component design
Security and authentication
Consistency models and replication
Message queues and async processing
Failure handling and fault tolerance
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 schema migrations with zero downtime?
- 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:
- Ability to process real-time payments globally for millions of users.
- Support multiple payment methods (credit card, bank transfer, digital wallets).
3...
Capacity Estimation
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To estimate capacity, we assume:
- Daily Transactions: 10 million
- Peak Transactions: 2,000 TPS
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Calculations:
- Average transaction size: 1 KB
- Total Data Throughp...
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