Merge pull request #42727 from robscott/gateway-v0.8.0

Adding Gateway API v0.8.0 Blog Post

Author: k8s-ci-robot

content/en/blog/_posts/2023-08-29-Gateway-API-v080.md

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+---
+layout: blog
+title: "Gateway API v0.8.0: Introducing Service Mesh Support"
+date: 2023-08-29T10:00:00-08:00
+slug: gateway-api-v0-8
+---
+
+***Authors:*** Flynn (Buoyant), John Howard (Google), Keith Mattix (Microsoft), Michael Beaumont (Kong), Mike Morris (independent), Rob Scott (Google)
+
+We are thrilled to announce the v0.8.0 release of Gateway API! With this
+release, Gateway API support for service mesh has reached [Experimental
+status][status]. We look forward to your feedback!
+
+We're especially delighted to announce that Kuma 2.3+, Linkerd 2.14+, and Istio
+1.16+ are all fully-conformant implementations of Gateway API service mesh
+support.
+
+## Service mesh support in Gateway API
+
+While the initial focus of Gateway API was always ingress (north-south)
+traffic, it was clear almost from the beginning that the same basic routing
+concepts should also be applicable to service mesh (east-west) traffic. In
+2022, the Gateway API subproject started the [GAMMA initiative][gamma], a
+dedicated vendor-neutral workstream, specifically to examine how best to fit
+service mesh support into the framework of the Gateway API resources, without
+requiring users of Gateway API to relearn everything they understand about the
+API.
+
+Over the last year, GAMMA has dug deeply into the challenges and possible
+solutions around using Gateway API for service mesh. The end result is a small
+number of [enhancement proposals][geps] that subsume many hours of thought and
+debate, and provide a minimum viable path to allow Gateway API to be used for
+service mesh.
+
+### How will mesh routing work when using Gateway API?
+
+You can find all the details in the [Gateway API Mesh routing
+documentation][mesh-routing] and [GEP-1426], but the short version for Gateway
+API v0.8.0 is that an HTTPRoute can now have a `parentRef` that is a Service,
+rather than just a Gateway. We anticipate future GEPs in this area as we gain
+more experience with service mesh use cases -- binding to a Service makes it
+possible to use the Gateway API with a service mesh, but there are several
+interesting use cases that remain difficult to cover.
+
+As an example, you might use an HTTPRoute to do an A-B test in the mesh as
+follows:
+
+```yaml
+apiVersion: gateway.networking.k8s.io/v1beta1
+kind: HTTPRoute
+metadata:
+  name: bar-route
+spec:
+  parentRefs:
+  - group: ""
+    kind: Service
+    name: demo-app
+    port: 5000
+  rules:
+  - matches:
+    - headers:
+      - type: Exact
+        name: env
+        value: v1
+    backendRefs:
+    - name: demo-app-v1
+      port: 5000
+  - backendRefs:
+    - name: demo-app-v2
+      port: 5000
+```
+
+Any request to port 5000 of the `demo-app` Service that has the header `env:
+v1` will be routed to `demo-app-v1`, while any request without that header
+will be routed to `demo-app-v2` -- and since this is being handled by the
+service mesh, not the ingress controller, the A/B test can happen anywhere in
+the application's call graph.
+
+### How do I know this will be truly portable?
+
+Gateway API has been investing heavily in conformance tests across all
+features it supports, and mesh is no exception. One of the challenges that the
+GAMMA initiative ran into is that many of these tests were strongly tied to
+the idea that a given implementation provides an ingress controller. Many
+service meshes don't, and requiring a GAMMA-conformant mesh to also implement
+an ingress controller seemed impractical at best. This resulted in work
+restarting on Gateway API _conformance profiles_, as discussed in [GEP-1709].
+
+The basic idea of conformance profiles is that we can define subsets of the
+Gateway API, and allow implementations to choose (and document) which subsets
+they conform to. GAMMA is adding a new profile, named `Mesh` and described in
+[GEP-1686], which checks only the mesh functionality as defined by GAMMA. At
+this point, Kuma 2.3+, Linkerd 2.14+, and Istio 1.16+ are all conformant with
+the `Mesh` profile.
+
+## What else is in Gateway API v0.8.0?
+
+This release is all about preparing Gateway API for the upcoming v1.0 release
+where HTTPRoute, Gateway, and GatewayClass will graduate to GA. There are two
+main changes related to this: CEL validation and API version changes.
+
+### CEL Validation
+
+The first major change is that Gateway API v0.8.0 is the start of a transition
+from webhook validation to [CEL validation][cel] using information built into
+the CRDs. That will mean different things depending on the version of
+Kubernetes you're using:
+
+#### Kubernetes 1.25+
+
+CEL validation is fully supported, and almost all validation is implemented in
+CEL. (The sole exception is that header names in header modifier filters can
+only do case-insensitive validation. There is more information in [issue
+2277].)
+
+We recommend _not_ using the validating webhook on these Kubernetes versions.
+
+#### Kubernetes 1.23 and 1.24
+
+CEL validation is not supported, but Gateway API v0.8.0 CRDs can still be
+installed. When you upgrade to Kubernetes 1.25+, the validation included in
+these CRDs will automatically take effect.
+
+We recommend continuing to use the validating webhook on these Kubernetes
+versions.
+
+#### Kubernetes 1.22 and older
+
+Gateway API only commits to support for [5 most recent versions of
+Kubernetes][supported-versions]. As such, these versions are no longer
+supported by Gateway API, and unfortunately Gateway API v0.8.0 cannot be
+installed on them, since CRDs containing CEL validation will be rejected.
+
+### API Version Changes
+
+As we prepare for a v1.0 release that will graduate Gateway, GatewayClass, and
+HTTPRoute to the `v1` API Version from `v1beta1`, we are continuing the process
+of moving away from `v1alpha2` for resources that have graduated to `v1beta1`.
+For more information on this change and everything else included in this
+release, refer to the [v0.8.0 release notes][v0.8.0 release notes].
+
+## How can I get started with Gateway API?
+
+Gateway API represents the future of load balancing, routing, and service mesh
+APIs in Kubernetes. There are already more than 20 [implementations][impl]
+available (including both ingress controllers and service meshes) and the list
+keeps growing.
+
+If you're interested in getting started with Gateway API, take a look at the
+[API concepts documentation][concepts] and check out some of the
+[Guides][guides] to try it out. Because this is a CRD-based API, you can
+install the latest version on any Kubernetes 1.23+ cluster.
+
+If you're specifically interested in helping to contribute to Gateway API, we
+would love to have you! Please feel free to [open a new issue][issue] on the
+repository, or join in the [discussions][disc]. Also check out the [community
+page][community] which includes links to the Slack channel and community
+meetings. We look forward to seeing you!!
+
+## Further Reading:
+
+- [GEP-1324] provides an overview of the GAMMA goals and some important
+  definitions. This GEP is well worth a read for its discussion of the problem
+  space.
+- [GEP-1426] defines how to use Gateway API route resources, such as
+  HTTPRoute, to manage traffic within a service mesh.
+- [GEP-1686] builds on the work of [GEP-1709] to define a _conformance
+  profile_ for service meshes to be declared conformant with Gateway API.
+
+Although these are [Experimental][status] patterns, note that they are available
+in the [`standard` release channel][ch], since the GAMMA initiative has not
+needed to introduce new resources or fields to date.
+
+[gamma]:https://gateway-api.sigs.k8s.io/concepts/gamma/
+[status]:https://gateway-api.sigs.k8s.io/geps/overview/#status
+[ch]:https://gateway-api.sigs.k8s.io/concepts/versioning/#release-channels-eg-experimental-standard
+[cel]:/docs/reference/using-api/cel/
+[crd]:/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/
+[concepts]:https://gateway-api.sigs.k8s.io/concepts/api-overview/
+[geps]:https://gateway-api.sigs.k8s.io/contributing/enhancement-requests/
+[guides]:https://gateway-api.sigs.k8s.io/guides/getting-started/
+[impl]:https://gateway-api.sigs.k8s.io/implementations/
+[install-crds]:https://gateway-api.sigs.k8s.io/guides/getting-started/#install-the-crds
+[issue]:https://github.com/kubernetes-sigs/gateway-api/issues/new/choose
+[disc]:https://github.com/kubernetes-sigs/gateway-api/discussions
+[community]:https://gateway-api.sigs.k8s.io/contributing/community/
+[mesh-routing]:https://gateway-api.sigs.k8s.io/concepts/gamma/#how-the-gateway-api-works-for-service-mesh
+[GEP-1426]:https://gateway-api.sigs.k8s.io/geps/gep-1426/
+[GEP-1324]:https://gateway-api.sigs.k8s.io/geps/gep-1324/
+[GEP-1686]:https://gateway-api.sigs.k8s.io/geps/gep-1686/
+[GEP-1709]:https://gateway-api.sigs.k8s.io/geps/gep-1709/
+[issue 2277]:https://github.com/kubernetes-sigs/gateway-api/issues/2277
+[supported-versions]:https://gateway-api.sigs.k8s.io/concepts/versioning/#supported-versions
+[v0.8.0 release notes]:https://github.com/kubernetes-sigs/gateway-api/releases/tag/v0.8.0
+[versioning docs]:https://gateway-api.sigs.k8s.io/concepts/versioning/