Design a real-time Authentication System
Last updated: September 13, 2025
Quick Overview
Design a real-time authentication system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Snowflake
September 13, 202533
15
1,896 solved
Design a real-time authentication system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Snowflake 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
- What monitoring and alerting would you set up on day one?
- How would you optimize costs as the system scales?
- How would you handle a region-wide outage?
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Requirements
- Functional Requirements:
- Real-time user authentication with support for multiple authentication methods (password, OAuth, MFA).
- Support for account creation, password reset, and session ...
Capacity Estimation
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Estimating QPS:
- Assume Snowflake has 100 million users, with 5% simultaneously trying to authenticate during peak times.
- This translates to 5 million QPS.
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Storage Needs:
- Each ...
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