Your company wants to split a large monolith into microservices. How would you approach it, and when would you argue against it?

What the interviewer wants to hear

• Start from the real problem: team scaling, deploy speed or scaling hotspots
• Find boundaries by business domain (bounded contexts) and data ownership
• Strangler fig: extract one service at a time behind a facade or gateway
• Each service owns its data; handle consistency with events or sagas
• Invest in CI/CD, observability and contracts first
• A modular monolith may be the better answer for small teams

Model answer

First I would ask what problem we are solving: many teams blocking each other on releases, one part needing very different scaling, or just a messy codebase. Messy code is not fixed by adding a network; a modular monolith with clear internal boundaries may be enough, especially for a small team. If we go ahead, I would map business domains and data ownership to find boundaries, then use the strangler fig pattern: put a gateway in front, extract one well-bounded area like notifications or billing, route its traffic to the new service, and repeat. Each service must own its database; shared tables bring back the coupling. Cross-service consistency then needs events, an outbox, and sagas instead of transactions. Before the first extraction I would invest in CI/CD, tracing, centralised logs and API contracts, because debugging distributed failures without them is very painful.

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