How the controller-runtime Cache Actually Works, and Why Your Controller Does Not Crash the API Server

The article explains how controller-runtime works in Kubernetes, specifically how it uses a local in-memory cache to read objects from the API. This design makes reads cheap but can lead to memory consumption, hidden O(n) scans, and stale reads. Engineers should understand this to avoid production issues. To avoid issues, remember that r.Get() and r.List() inside a reconciler read from the local cache, not the API server.