/ The Arena

Problem Overview

In distributed event-driven systems, updating a database and publishing a message to Apache Kafka in the same HTTP handler is vulnerable to the Dual-Write Problem.

To guarantee At-Least-Once Delivery on the producer side and Idempotent Exactly-Once Processing on the consumer side, you will implement:

1. A Transactional Outbox Relay Engine simulating PostgreSQL SELECT ... FOR UPDATE SKIP LOCKED worker concurrency.
2. An Exponential Backoff Retry Handler for transient Kafka broker failures.
3. A Transactional Inbox Deduplication Engine ensuring consumers process each event at most once per consumer group.