Kubernetes Operators is the correct option.

Kubernetes Operators encapsulate application specific operational knowledge and implement custom controllers that can perform ordered and predictable scaling for stateful workloads. Operators can manage StatefulSets and external resources together and they can enforce policies such as ordered startup, graceful shutdown, and coordinated configuration changes while scaling. That level of application aware control is required when you need predictable and controlled scaling for stateful services.

Vertical Pod Autoscaler (VPA) is incorrect because it adjusts pod resource requests and limits rather than the number of replicas. Vertical Pod Autoscaler (VPA) may require pod restarts to change resources and it does not provide ordered or application aware replica lifecycle management needed for complex stateful systems.

Cluster Autoscaler is incorrect because it scales cluster nodes in response to pending pods and not the application replicas themselves. Cluster Autoscaler provides node capacity but it cannot implement application specific, ordered, or safe scaling policies for stateful workloads.

Custom Resource Definitions is incorrect because CRDs are a mechanism to extend the Kubernetes API and they do not by themselves implement scaling logic. Custom Resource Definitions are often used as the API surface for an Operator, but the CRD alone is just the data model and not the controller that enforces predictable scaling.

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