Cutting API Failures by 90%, a .NET 9 Event-Driven Cloud Breakthrough

TL;DR — We swapped Mattrx's inter-service REST calls for Kafka topics (multi-tenant marketing analytics SaaS, .NET 9 / ASP.NET Core, Azure SQL, ~3,200 req/sec peak). Over 8 weeks: end-to-end ingestion failures 1.9% → 0.18% (−90%), ingestion p95 180 ms → 8 ms (−96%), events lost on downstream outage