Design a high-throughput Authentication System
Last updated: November 2, 2025
Quick Overview
Design a high-throughput authentication system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Mastercard
System Design
Software Engineer
Mastercard
November 2, 2025Software Engineer
Technical Screen
System Design
Medium
184
10
4,005 solved
Design a high-throughput authentication system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Mastercard 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
High-level architecture and component design
Load balancing and horizontal scaling
Security and authentication
Monitoring, logging, and alerting
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 do you ensure data consistency across multiple services?
- What monitoring and alerting would you set up on day one?
- How would you handle schema migrations with zero downtime?
- How would you migrate from a monolithic to a microservices architecture?
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Requirements
- Functional Requirements:
- Authenticate users through multiple methods (e.g., username/password, biometrics, OTP).
- Support for high throughput, capable of processing millions of authen...
Capacity Estimation
- Estimating QPS:
- Assume 100 million users, with each user making an average of 2 authentication requests per day.
- Total daily requests: 100 million * 2 = 200 million requests/day.
...
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