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Brownfield System Design Interviews: How to Answer Migration and Legacy Questions
TL;DR: Migration prompts reveal how to move from legacy to new services without downtime, emphasizing risk sequencing and respect for the existing system.
The article argues that senior interviews increasingly use ten-year-old monolith migration prompts rather than greenfield designs. It highlights three evaluation aspects: sequencing risk so each step remains reversible and non-catastrophic, maintaining value delivery throughout the process, and showing respect for legacy constraints and business rules. It also positions migration problems as more representative of real work than greenfield problems, since most teams renovate occupied systems. The piece offers a practical method for answering migration questions and emphasizes preparation grounded in real-world constraints.
Question for the room: What has been your most challenging migration sequencing decision, and how did you ensure reversibility and business value at each step?
— via dev.to
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