You design service boundaries along domain lines. They cut across three existing teams. What happens and what do you do?

What the interviewer is testing

Whether you treat organisational structure as a real constraint rather than an inconvenience.

What happens

Conway's law asserts itself. A design that cuts across the org chart is fought by gravity for its entire life:

Every change to a service requires coordination between three teams, so lead time rises and ownership becomes ambiguous. When something breaks at 3 AM, it is unclear who is called. Under delivery pressure teams add functionality where it is easiest for them rather than where it belongs, so the boundaries erode. Within eighteen months the system has drifted back towards the team structure.

This happens regardless of how correct the domain boundaries are.

The options

Change the teams to match the architecture — the inverse Conway manoeuvre. It works, and it needs authority most architects lack. If you can secure it, this is the strongest answer: reshape teams around the domains, then let the architecture follow.

Change the architecture to match the teams. Less satisfying and frequently more successful. A boundary that aligns with an existing team will be maintained; one that does not will erode. A slightly worse boundary that survives beats a better one that decays.

Assign clear ownership within the current structure — one team owns each service outright, with the others as consumers through explicit contracts. Workable if the domain and team boundaries are close enough that a single team can genuinely own each service.

The recommendation

Raise it explicitly rather than designing past it. Present the design alongside the organisational change it implies, and let leadership decide. If the reorganisation is not possible, adjust the architecture consciously and record why — rather than shipping a design that will be fought and then being surprised when it drifts.

What a strong answer adds

Cognitive load as the framing that makes this concrete for leadership: boundaries should be drawn so a team's total load fits. That turns an abstract argument about Conway's law into a discussion about whether teams can sustainably own what they are being given, which is a conversation leadership engages with.

Common weak answers

Designing the correct boundaries and expecting the organisation to adapt. Ignoring the constraint and attributing the later erosion to discipline.