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Operator: CRD Plus a Reconcile Loop

A CRD gives us a new data type, but creating a custom resource makes nothing happen. An operator joins a CRD with a controller running a loop: it watches the custom resource and acts to bring reality in line with desire. This article builds a real operator from scratch — an Echo CRD and an in-pod controller — then watches it create a Deployment when we create an Echo, scale when we edit replicas, and let the Deployment be cleaned up when we delete the Echo.