Support Multi-Cluster Services using ServiceImport as a BackendRef

[danehans]

As a Kubernetes cluster administrator, I would like Gateway to support Kubernetes services that run in multiple clusters. Gateway should support multi-cluster service networking methods defined by sig-multicluster but not preclude other methods.

xref: #7

[danehans]

xref: #36

[arkodg]

related #16 (comment)

[danehans]

From #16 (comment)

... Will there be a meta controller? Will each bootstrap have to manually point at multiple config sources with distributed policy? Etc.

At a high-level, we should consider leveraging the multi-cluster services (MCS) APIs. For example, an Infra Admin can use ServiceImport/ServiceExport resources to create multi-cluster services. A separate ingress cluster with Envoy Gateway(s) can load balance to the multi-cluster services by using a ServiceImport as the backendRef of an HTTPRoute.

[arkodg]

linking relevant upstream Gateway API design proposal on using ServiceImport as a valid BackendRef
https://docs.google.com/document/d/1akwzBKtMKkkUV8tX-O7tPcI4BPMOLZ-gmS7Iz-7AOQE/edit#

[arkodg]

supporting ServiceImport in Gateway API has transitioned to experimental https://gateway-api.sigs.k8s.io/geps/gep-1748/ and this project should implement this API soon

[Xunzhuo]

kubernetes-sigs/gateway-api#1922

Make it extented now