Plugin: Gateway API

[iRaindrop]

Need topic to install Gateway-API plugin.

Content derived from https://gateway-api.sigs.k8s.io/guides/

Proposed Changes

• Create Installing Gateway API to include in the Plugin section for Installing Knative.

[knative-prow]

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[Cali0707]

/cc @dprotaso

[dprotaso]

There's a lot of duplicate content that's from the Gateway API website. I don't think we should manually mirror such content here given that it changes all the time.

[evankanderson]

/assign

[evankanderson]

This should be documenting installing the Knative networking adapter for Gateway API.

I don't know if a picture is helpful, but here's some mermaid that might clarify:

flowchart TB
 subgraph s1["Gateway API"]
    HR[HTTPRoute]
    GW[Gateway listener]
  end
  KSvc["Knative Service"] -- owns --> Route
  Route -- creates --> HR
  Route -- creates --> GW

For this, we're talking about the component that implements the "creates"

[evankanderson]

We should link to the Gateway API top-level guide, rather than duplicating all of the sub-guides. I think https://gateway-api.sigs.k8s.io/implementations/ is probably the best page for linking to the options (yes, there are more than a dozen GA implementations).

[evankanderson]

Some of these guides are for unrelated topics (TCP routing, for instance, is not relevant to Knative's scaling model).

[evankanderson]

These should cover installing https://github.com/knative-extensions/net-gateway-api

This should probably use a snippet like:

    1. Install the Knative Gateway API controller by running the command:
      ```bash
      kubectl apply -f {{ artifact(repo="net-gateway-api",org="knative-extensions",file="net-gateawy-api.yaml")}}
      ```

    1. Configure Knative Serving to use Gateway API by default by running the command:
      ```bash
      kubectl patch configmap/config-network \
        --namespace knative-serving \
        --type merge \
        --patch '{"data":{"ingress-class":"gateway-api.ingress.networking.knative.dev"}}'

And then using kubectl get gateway --all-namespaces to find the IP address of the gateway. This configuration will also need to be incorporated into the config-gateway ConfigMap to find the external and within-cluster (local) gateways. I'm not sure whether that's well-documented anywhere, but it's the "istio-system" part of the "gateway" sub-key of the gateway class.

It's probably worth calling out that Istio and Contour are the currently-tested implementations, but that other Gateway API implementations should work. https://github.com/knative-extensions/net-gateway-api/blob/main/docs/test-version.md has some additional information that it may be worth incorporating or linking.

Configuration for the installation is here:

https://github.com/knative-extensions/net-gateway-api/blob/main/config/config-gateway.yaml