Kubernetes Gateway API

Kuma supports Kubernetes Gateway API for configuring built-in gateway as well as traffic routing using the experimental GAMMA routing spec.

Installation

Checkout our dedicated installation guide.

Customization

Gateway API provides the parametersRef field on GatewayClass.spec to provide additional, implementation-specific configuration to Gateways. When using Gateway API with Kuma, you can refer to a MeshGatewayConfig resource:

apiVersion: gateway.networking.k8s.io/v1
kind: GatewayClass
metadata:
  name: kuma
spec:
  controllerName: gateways.kuma.io/controller
  parametersRef:
    kind: MeshGatewayConfig
    group: kuma.io
    name: kuma

This resource has the same structure as the MeshGatewayInstance resource except that the tags field is optional. With a MeshGatewayConfig you can then customize the generated Service and Deployment resources.

Multi-mesh

You can specify a Mesh for Gateway and HTTPRoute resources by setting the kuma.io/mesh annotation Note that HTTPRoutes must also have the annotation to reference a Gateway from a non-default Mesh.

Cross-mesh

Cross-mesh gateways are supported with Gateway API. You’ll just need to create a corresponding GatewayClass pointing to a MeshGatewayConfig that sets crossMesh: true:

apiVersion: gateway.networking.k8s.io/v1
kind: GatewayClass
metadata:
  name: kuma-cross-mesh
spec:
  controllerName: gateways.kuma.io/controller
  parametersRef:
    group: kuma.io
    kind: MeshGatewayConfig
    name: default-cross-mesh
---
apiVersion: kuma.io/v1alpha1
kind: MeshGatewayConfig
metadata:
  name: default-cross-mesh
spec:
  crossMesh: true

and then reference it in your Gateway:

apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: kuma
  namespace: default
spec:
  gatewayClassName: kuma-cross-mesh
  listeners:
  - name: proxy
    port: 8080
    protocol: HTTP

Multi-zone Deployments

The Gateway API supports multi-zone deployments, but with some limitations:

• Gateway API resources like Gateway, ReferenceGrant, and HTTPRoute must be created in non-global zones.

• Only services deployed within the same Kubernetes cluster, such as the HTTPRoute, can be referenced via backendRef.

  Important Note: This limitation exist because, Kuma currently only allows referencing as backendRefs Kubernetes Services.

  This is a temporary limitation. We’re actively working on extending backendRef to support Kuma’s MeshServices. Once this feature is complete, you’ll be able to reference services across different clusters within your mesh.

  To better visualize this limitation here’s an example scenario that describes how you could configure multi-zone deployments with the Gateway API. In this example, you have the following resources:

  • Two zones (zone-1 and zone-2) in separate Kubernetes clusters

  • Gateway with listener on port 8080 deployed in zone-1

  • Two services:

    • A service named backend deployed in each zone

    • A service named db deployed only in zone-2

   
   flowchart TD
       subgraph c2["k8s-cluster-2"]
           subgraph z2["zone-2"]
               subgraph c1z2s1["Service"]
                   b2(backend)
               end
               subgraph c1z2s2["Service"]
                   db(db)
               end
           end
       end
       subgraph c1["k8s-cluster-1"]
           subgraph z1["zone-1"]
               subgraph Gateway
                   listener(:8080)
               end
               subgraph Service
                   b1(backend)
               end
           end
       end
     

  If you deploy multi-zone with Gateway API, the following will occur:

  • If you create an HTTPRoute with a backendRef targeting the backend service in k8s-cluster-1, it will only route traffic to the backend service in k8s-cluster-1.

   
   flowchart TD
       subgraph c2["k8s-cluster-2"]
           subgraph z2["zone-2"]
               subgraph c1z2s1["Service"]
                   backend2(backend)
               end
               subgraph c1z2s2["Service"]
                   db(db)
               end
           end
       end
       subgraph c1["k8s-cluster-1"]
           subgraph z1["zone-1"]
               subgraph Service
                   backend1(backend)
               end
               subgraph Gateway
                   listener(:8080)
               end
               subgraph HTTPRoute
                   route1(/)
               end
               route1--"❌"-->backend2
               linkStyle 0 stroke:red,color:red,stroke-dasharray: 5 5;
               route1-->backend1
               listener-->route1
           end
       end
     

  • Similarly, if you create an HTTPRoute with a backendRef pointing to the db service in k8s-cluster-1, it will result in a HTTPRoute with a ResolvedRefs status condition of BackendNotFound because service db is not present in k8s-cluster-1.

   
   flowchart TD
       subgraph c2["k8s-cluster-2"]
           subgraph z2["zone-2"]
               subgraph c1z2s1["Service"]
                   backend2(backend)
               end
               subgraph c1z2s2["Service"]
                   db(db)
               end
           end
       end
       subgraph c1["k8s-cluster-1"]
           subgraph z1["zone-1"]
               subgraph Gateway
                   listener(:8080)
               end
               subgraph HTTPRoute
                   route1(/)
               end
               subgraph Service
                   backend1(backend)
               end
               route1--"❌"-->db
               linkStyle 0 stroke:red,color:red,stroke-dasharray: 5 5;
               listener-->route1
           end
       end
     

Service to service routing

Kuma also supports routing between services with HTTPRoute in conformance with the GAMMA specifications.

GAMMA is a Gateway API subproject focused on mesh implementations of Gateway API and extending the Gateway API resources to mesh use cases.

The key feature of HTTPRoute for mesh routing is specifying a Kubernetes Service as the parentRef, as opposed to a Gateway. All requests to this Service are then filtered and routed as specified in the HTTPRoute.

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: canary-demo-app
  namespace: kuma-demo
spec:
  parentRefs:
  - name: demo-app
    port: 5000
    kind: Service
  rules:
  - backendRefs:
    - name: demo-app-v1
      port: 5000
    - name: demo-app-v2
      port: 5000

The namespace of the HTTPRoute is key. If the route’s namespace and the parentRef’s namespace are identical, Kuma applies the route to requests from all workloads. If the route’s namespace differs from its parentRef’s namespace, the HTTPRoute applies only to requests from workloads in the route’s namespace.

How it works

Kuma includes controllers that reconcile Gateway API CRDs and convert them into the corresponding Kuma CRDs. This is why in the GUI, Kuma MeshGateways/MeshHTTPRoutes/MeshTCPRoutes are visible and not Kubernetes Gateway API resources.

Kubernetes Gateway API resources serve as the source of truth for Kuma gateways and routes. Any edits to the corresponding Kuma resources are overwritten.