The Acknowledgment Gap - How Event-Driven Systems Lose Messages Without Errors

This article delves into a dangerous failure mode in event-driven systems where components report success for operations that are only accepted, not completed, leading to silent message loss without errors or alerts. It discusses the gap between 'accepted' and 'completed' acknowledgments, using examples from queue consumers, async APIs, and workflow engines. The author shares a real debugging experience and explains how offset-based consumer groups can exacerbate this issue. The piece provides first-principles analysis and strategies to close this acknowledgment gap, making it valuable for developers building reliable distributed systems.