An ack to Pub/Sub is a delete command, not a proof of processing. With the workflow engine in the ack path and a correlation that rejects, the place of the ack decides between standstill and data loss. The complete tutorial: nack with dead-letter topic, transactional inbox, a relay without the ordering trap, plus a decision table.
An online tool shop ends expired promotions overnight. The job reports 412 hits and the shop keeps selling at the promo price. Three annotations on the repository interface are behind it: two reach deep into Hibernate, one does nothing at all. The complete tutorial on readOnly, @Modifying and where the transaction boundary belongs. As of Spring Boot 4.
Fourteen line items of a goods receipt stopped dead, with no error and no incident. A signal only reaches whoever is already waiting when it is thrown, and an asynchronous step sat right before that. This tutorial rebuilds the case with Flowable 8, shows it in a test, repairs the stuck instances and replaces the broadcast with an addressed message.
A rollout runs through cleanly, every pod is Ready, and yet requests get lost. Why deregistration runs in parallel to the shutdown, why only POST is affected, and how the preStop hook, the grace period and graceful shutdown have to fit together.
A service that returns nothing but errors looks exactly like a service with no traffic. Why that happens, how a zero series derived from the denominator fixes it, why vector(0) is not enough, and what dashboard and alert rule look like in Terraform.
A green deploy proves the service starts, nothing more. Using an order service as the example, this article walks the path to production readiness as a risk-driven process in four rounds: functional correctness, law and tax, security and operations. With the AI trap where tests only mirror the code, and arc42 as the frame.
