Support for Gateway APIs

[ecordell]

Describe the feature

Many ingress solutions now provide the gateway api or seem likely to in the future. Current providers (from the docs) include Istio, Contour, Traefik, Kong, Emissary, Consul, and GKE ingress.

The Gateway API supports a weight field on BackendRef. If Flagger supported the Gateway APIs, it could potentially just work™️ with a large set of ingress providers going forward.

This would allow the same flagger configuration for a service to continue working even if the ingress provider changes over time (because the APIs flagger is configuring will remain the same across providers).

Proposed solution

Support the Gateway API as a "mesh provider", using the weight on BackendRef's to provide canary deployments.

Any alternatives you've considered?

Although many projects now support the Gateway API, I am personally not up to speed on the overall state of that community and whether we should expect Gateway API support to continue to be developed and reach a stable v1 API. But I think the same concern applies to any of the currently-supported mesh providers as well.

[stefanprodan]

Yes this is on the roadmap cfd2ff9#diff-b335630551682c19a781afebcf4d07bf978fb1f8ac04c6bf87428ed5106870f5

I should update the name, as now is called Gateway API.