You must explain the same decision — moving from a monolith to services for one domain — to a CFO, an engineering manager and an engineer. What changes?
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What the interviewer is testing
Whether you can genuinely re-frame rather than varying the level of detail.
To the CFO
Outcome, cost, risk, timeline. "The checkout domain is where our releases fail most often and where a defect costs revenue directly. Separating it lets that team release independently. Cost is about two quarters of one team's time plus a modest infrastructure increase. The risk of not doing it is that release velocity in this area continues to decline and each incident costs roughly this much."
No technology. The word "microservices" should not appear.
To the engineering manager
Delivery impact, team capability, operational burden, sequencing. "This team gains independent deployment, which removes the coordination that currently costs them a week per release. It requires them to take on their own on-call for the service and to learn the deployment platform. The migration runs alongside feature work for two quarters, so their delivery rate drops by about a third in that period. The riskiest step is splitting the data, and we do that first while we still have room to change course."
To the engineer
Mechanism and consequence. Where the boundary falls and why, how the data is separated, what becomes eventually consistent and what that means for the checkout flow, what happens when the service is unavailable, how the transaction that currently spans both is decomposed, and what the migration sequence is.
What is common to all three
The recommendation, stated up front, and what would change it. Presenting options without a recommendation reads as an abdication to every one of these audiences.
What a strong answer adds
Preparing the one sentence you want repeated in the meeting you are not in. That is what actually travels through an organisation, and it should be drafted deliberately rather than left to chance.
Common weak answers
The same explanation at three levels of technical detail. Leading with the architecture in every version.