When a Spring Boot service needs to talk to another service without waiting on a synchronous HTTP call, message queues are the usual answer. Apache Kafka has become the default choice for this in most backend teams, but a lot of tutorials stop at a "hello world" producer and consumer that would never survive a real production load. Things like consumer retries, error handling, serialization of real objects, and graceful shutdown get skipped, and those are exactly the parts that page you at 2 a.m...