GEP: Gateway Routability

[dprotaso]

Discussed in #1247

^{Originally posted by evankanderson June 30, 2022}
Currently, the GatewayAddress field supports only external (LoadBalanced) Gateway definitions. I'd like to suggest adding a ClusterLocal or ClusterIP AddressType with Extended support (like the existing IPAddress and Hostname support).

One of the early feature requests for Knative was the ability to deploy an application using Knative's HTTP routing support, but make it only available within the cluster. I want to be able to specify both the "internal" (service.namespace.svc) and "external" (service.namespace.example.com) Gateways using the same GatewayClass on the cluster, but ensure that the "internal" service is only reachable within the cluster. This would greatly simplify deployment for users over the instructions we have today.