Zettabyte·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say

Jun 2026

Summary

Had a system design round at Zettabyte for a full-stack role and the middleware question took up most of the session. More depth than I expected for what I assumed would be a surface-level topic.

Questions Asked (1)

Walk me through how you design and use middleware in your applications, including ordering, custom implementations, and how you test it.

System DesignTechnical Trade-offsAPI & Integrations

Author's notes

I started with the textbook definition and immediately felt like I was reciting a glossary.

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AI HintsAI Generated

Suggested Approach

Start by defining middleware's role in your architecture, then walk through a concrete example of designing a middleware pipeline with attention to ordering and custom implementations. Finish by explaining your testing strategy, emphasizing how you isolate middleware and verify behavior under realistic conditions.

Pro tip: Show that you treat middleware as a cross-cutting concern with clear contracts and observability—mention how you log, trace, and monitor middleware to catch issues in production, not just in tests.

1. Define middleware's purpose and scope

Explain what middleware is in your context (e.g., request/response processing, authentication, logging) and why you use it to keep concerns separated and reusable.

2. Design the pipeline and ordering

Describe how you determine the order of middleware (e.g., authentication before authorization, logging early) and the trade-offs involved, such as performance vs. security.

3. Implement custom middleware

Walk through a specific custom middleware you built, its interface, how it handles errors, and how it interacts with the rest of the pipeline.

4. Test middleware in isolation and integration

Explain your testing approach: unit tests for individual middleware, integration tests for the pipeline, and how you mock dependencies and simulate edge cases.

5. Monitor and iterate

Discuss how you observe middleware in production (metrics, logs, traces) and use that feedback to refine ordering or implementation.

Key Points to Mention

Middleware ordering principles and common pitfalls (e.g., short-circuiting, error handling)
Custom middleware design: interface, error propagation, and composability
Testing strategies: unit tests with mocks, integration tests, and contract tests
Performance considerations: overhead, async handling, and caching
Observability: logging, tracing, and metrics for middleware
Trade-offs: flexibility vs. complexity, and when to avoid middleware

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.