After writing an order to the database, a service has to publish an event to a message broker. How do you guarantee the event isn't lost and that redelivering it doesn't duplicate the effect?
~4 min by voice
How to approach it
They're checking whether the candidate understands the problem of dual writes to a database and a broker, and can assemble a reliable chain: a transactional outbox for delivery, an idempotent consumer against duplicates, ordering, failure handling and monitoring. They also look at whether the candidate understands that end-to-end exactly-once doesn't exist.
The interviewer will ask this question and listen. Think out loud and ask for a hint if you need one. When you're done, pause or tap “That's my answer”. In about a minute, your score and the points you covered show up here.