Defending a decision under challenge, articulating what you gave up, and reasoning about reversibility.
4 questions in Architecture & Tech Leadership.
A synchronous call couples availability and latency but keeps the outcome knowable at the point of decision; an event decouples both but converts every failure into something the caller will never learn about. Choose by asking whether the caller needs the answer to proceed, not by which style is fashionable.
One PostgreSQL primary with a replica and tested backups is the strongest answer when a capacity estimate built from the prompt fits it with headroom and the core invariants need transactions. It ends the interview when the prompt rules it out, or when you use it to decline the distributed design you were asked for.
The choice turns on team topology and independent deployability, whether domain boundaries are stable, data ownership and distributed-transaction cost, and real operational maturity. Default to a modular monolith with enforced internal boundaries and extract services only on evidence.
Name the single writer first, then choose which coupling you would rather own: a shared schema couples the two teams' release calendars, while a replicated copy couples them to a staleness window and obliges someone to detect and repair divergence. Both are permanent, so pick the one your organisation can pay for.