How would you answer an interview scenario involving Observer pattern?

For an interview scenario involving Observer pattern, I would first clarify the business goal, scale, constraints, and the failure or quality attribute the interviewer wants to explore. Observer allows interested consumers to react when a subject publishes state changes or events. In this scenario, a domain event must update notifications and analytics. Explain when an in-process observer is enough and when messaging is preferable. For production, choose synchronous or asynchronous delivery deliberately, manage subscriptions, handle failures, and use durable messaging for cross-service reliability. I would then explain the main alternatives and tradeoffs, identify likely failure modes, and describe how I would validate the solution through testing, observability, security controls, and recovery or rollback planning.