You can't configure your Ingress to serve static data (from your host files for example) alone because the Ingress resource is just a way to configure a way of understanding for Kubernetes on how to access a specific internal resource from outside the cluster.
An API object that manages external access to the services in a cluster, typically HTTP.
This is more of an opinion based question but let me try to answer it.
installing Prometheus itself in the very same k8s cluster (as another running set of pods) is a normal thing.Am I right or just got a wrong idea from my research?
Considering good practices, shouldn't the monitoring tool be outside of the system that you actually intend to monitor?