Design a large-scale Authentication Platform
Last updated: August 16, 2025
Quick Overview
Design a geo-distributed authentication system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Zillow
August 16, 20250
12
2,536 solved
Design a geo-distributed authentication system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Zillow 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 schema migrations with zero downtime?
- How would you migrate from a monolithic to a microservices architecture?
- What would the deployment pipeline look like for this system?
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Requirements
Functional Requirements
- User Registration: Users must be able to register with email and password, or via social logins (Google, Facebook).
- User Authentication: The system must valid...
Capacity Estimation
To estimate the capacity needed:
- User Base: Assume 50 million users with 10% active at peak times.
- QPS Calculation: At peak, with 10% of users active, we can expect 5 million requests per ...
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