Question
Design a notification service.

While solving the problem, for idempotency handling, I have used even-driven architecture.
The solution that I gave is publishing the messages in Kafka, and processing the messages through Flink. So that unique message gets processed exactly once, with respect to the idempotent id.

Interviewer's (Staff Software Engineer) comments

1. There is no way to handle idempotency using even driven architecture.
2. He was expecting solution with Redis. (Synchronous write-through caching)

I did some research, my solution is working and much-more scalable in case of burst traffic and bust notification.

I got rejected.

Was I correct?