Build a geo-distributed Authentication Pipeline

Last updated: August 14, 2025

Quick Overview

Design a geo-distributed authentication system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.

Brex
Software Engineering Fundamentals
Software Engineer
Brex
August 14, 2025
Software Engineer
Onsite
Software Engineering Fundamentals
Medium

28

2

4,871 solved


Design a geo-distributed authentication system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.

This fundamentals question from Brex's Onsite 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
Concurrency and thread safety
Version control and branching strategies
API design and RESTful conventions
System observability and debugging
CI/CD pipelines
How to Approach This
  1. Apply SOLID principles. Single Responsibility makes code testable, Open/Closed makes it extensible.
  2. Choose data structures based on access patterns, not familiarity.
  3. Prefer immutable data and message passing over shared mutable state for concurrency.
  4. Design APIs with RESTful conventions, versioning, meaningful errors, and pagination from day one.
Possible Follow-up Questions
  • What are the security implications of this design?
  • How would you measure the performance of this component in production?
  • How would you document this for other engineers?
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Sample Answer
Core Principles

Start by identifying which engineering principles are most relevant: **SOLID Principles**: Single Responsibility (one reason to change), Open/Closed ...

Design Approach

**API Design**: Define clear interfaces before implementation. Use RESTful conventions for HTTP APIs. Version your APIs from the start. Return meaning...


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