Architect a real-time Authentication Engine
Last updated: September 16, 2025
Quick Overview
Design a real-time authentication system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Redfin
September 16, 20256
14
2,370 solved
Design a real-time authentication system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This fundamentals question from Redfin's Technical Screen tests whether you can reason about software design at a deep level. The interviewer expects discussion of maintainability, testability, and operational considerations.
What the Interviewer Expects
- Apply engineering principles to a realistic design scenario
- Discuss trade-offs between different approaches with concrete examples
- Demonstrate understanding of testability, maintainability, and extensibility
- Connect theoretical concepts to production engineering practices
- Discuss how the approach scales with team and codebase size
Key Topics to Cover
How to Approach This
- Apply SOLID principles. Single Responsibility makes code testable, Open/Closed makes it extensible.
- Choose data structures based on access patterns, not familiarity.
- Prefer immutable data and message passing over shared mutable state for concurrency.
- Design APIs with RESTful conventions, versioning, meaningful errors, and pagination from day one.
Possible Follow-up Questions
- How would you measure the performance of this component in production?
- What testing strategy would you use for this component?
- How would you handle backward compatibility?
- How would this design change if the team size doubled?
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Core Design Principles
For the real-time authentication engine at Redfin, the following core design principles apply:
- Single Responsibility Principle: Each module should have one reason to change. For instance, authe...
Architecture
The architecture for the real-time authentication engine will follow a microservices approach:
- Service Layer: A dedicated authentication service that exposes a RESTful API for login and token ma...
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