Conquer the CKAD Challenge 2025: Unleash Your Kubernetes Power!

Ingress rules are defined in the `rules` section of the Ingress spec because this section specifically outlines how external HTTP(S) traffic should be routed to services within a Kubernetes cluster. Each rule can specify a variety of parameters such as the host, paths, and backend services that should respond to the traffic. This enables more granular traffic management and control over how requests are handled and routed, which is essential for directing users to the correct application services based on the incoming request details.

The other options do not provide a coherent way to define Ingress rules. A separate configuration file might be used to organize resources, but the actual rules must be specified within the Ingress resource itself. Annotations on services may provide additional metadata or configurations but do not represent the routing rules. The `ingressClassName` attribute relates to the controller that will handle the ingress rules and does not define the rules themselves.