When Event-Driven Systems Become the Source of Truth: Lessons from CDC, Kafka, and Replay-Safe Inventory Platforms

Abstract

This paper examines the point at which event streams stop being helpful integration plumbing and become operational truth for business-critical state. Using CDC, Kafka and replay-safe inventory platforms as the frame, it focuses on the failures that matter after the brokers are healthy: ambiguous replay intervals, duplicate business effects, stale projections, ordering mistakes, weak idempotency boundaries and recovery jobs that finish without proving correctness. The central argument is that reliability in event-driven systems is not only a question of uptime or message delivery. Once downstream systems trust derived state, teams need explicit contracts for event identity, ordering, idempotency keys, dedupe horizons, CDC and outbox boundaries, replay controls, audit evidence and reconciliation. Readers leave with a practical way to judge whether retained events can repair business state without corrupting the systems that depend on it. Keeping events makes recovery possible. Boundaries and proof make recovery trustworthy.