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Gateway API v0.8.0: Introducing Service Mesh Support!

August 29, 2023 ยท 5 min read

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, and we've also made some smaller additions such as CEL validation. 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 the 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, 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 the Gateway API for service mesh. The end result is a small number of enhancement proposals that subsume many hours of thought and debate, and provide a minimum viable path to allow the Gateway API to be used for service mesh.

How will mesh routing work when using the Gateway API?

You can find all the details in the Gateway API Mesh routing documentation 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:

  kind: HTTPRoute
    name: bar-route
    - group: ""
      kind: Service
      name: demo-app
      port: 5000
    - matches:
      - headers:
        - type: Exact
          name: env
          value: v1
      - 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 GEP process 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 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. 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.

GEP Process Changes

The second significant change in Gateway API v0.8.0 is that we have (by necessity) taken a hard look at the process around Experimental GEPs. Some of these GEPs have been lingering long enough that projects have come to rely on them in production use, which is a bit of a breakdown of the GEP process. In order to prevent it happening in the future, we have changed the GEP process such that reaching Experimental requires that a GEP include both the graduation criteria by which the GEP will become Standard, and a probationary period after which the GEP will be dropped if does not meet its graduation criteria.

For an exhaustive list of changes included in the v0.8.0 release, please see the v0.8.0 release notes. For more information on Gateway API versioning, refer to the official documentation.

How can I get started with the Gateway API?

Gateway API represents the future of load balancing, routing, and service mesh APIs in Kubernetes. There are already more than 20 implementations 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 and check out some of the 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 on the repository, or join in the discussions. Also check out the community page 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 the Gateway API.

Although these are Experimental patterns, note that they are available in the standard release channel, since the GAMMA initiative has not needed to introduce new resources or fields to date.