ReferenceGrant¶

ReferenceGrant enables cross-namespace backend references in HTTPRoute and GRPCRoute resources. This is a security feature that requires explicit permission for a Route in one namespace to reference a Service in another namespace.

How It Works¶

ReferenceGrant must be created in the target namespace (where the Service is)
It grants permission to routes in the source namespace to reference Services in the target namespace
Without a ReferenceGrant, cross-namespace backend references are denied with ResolvedRefs=False status

flowchart LR
    subgraph app-namespace
        HR[HTTPRoute]
    end

    subgraph backend-namespace
        RG[ReferenceGrant]
        SVC[Service]
    end

    HR -->|references| SVC
    RG -->|allows| HR

Basic Example¶

---
# ReferenceGrant must be in the target namespace (where the Service is)
apiVersion: gateway.networking.k8s.io/v1beta1
kind: ReferenceGrant
metadata:
  name: allow-app-to-backend
  namespace: backend-namespace  # Target namespace
spec:
  from:
    - group: gateway.networking.k8s.io
      kind: HTTPRoute
      namespace: app-namespace  # Source namespace
  to:
    - group: ""  # Core API group (empty string for Services)
      kind: Service
---
# HTTPRoute in source namespace
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: cross-ns-route
  namespace: app-namespace
spec:
  parentRefs:
    - name: cloudflare-tunnel
      namespace: cloudflare-tunnel-system
  hostnames:
    - myapp.example.com
  rules:
    - backendRefs:
        - name: backend-service
          namespace: backend-namespace  # Cross-namespace reference
          port: 8080

Field Reference¶

`spec.from` (required)¶

Defines which resources can reference targets in this namespace.

Field	Description
`group`	API group of the referencing resource (e.g., `gateway.networking.k8s.io`)
`kind`	Kind of the referencing resource (`HTTPRoute` or `GRPCRoute`)
`namespace`	Namespace of the referencing resource

`spec.to` (required)¶

Defines which resources can be referenced.

Field	Description
`group`	API group of the target resource (`""` for core/Services)
`kind`	Kind of the target resource (`Service`)
`name`	Optional: specific resource name (if omitted, all resources of this kind are allowed)

Allow All Namespaces¶

To allow any namespace to reference Services in this namespace:

apiVersion: gateway.networking.k8s.io/v1beta1
kind: ReferenceGrant
metadata:
  name: allow-all-namespaces
  namespace: shared-services
spec:
  from:
    - group: gateway.networking.k8s.io
      kind: HTTPRoute
      namespace: "*"  # Not supported - use multiple entries
  to:
    - group: ""
      kind: Service

Wildcard Not Supported

The Gateway API does not support wildcards in namespace. You must create individual entries for each namespace, or create the ReferenceGrant in each source namespace.

Allow Specific Service¶

Restrict access to a specific Service:

apiVersion: gateway.networking.k8s.io/v1beta1
kind: ReferenceGrant
metadata:
  name: allow-specific-service
  namespace: backend-namespace
spec:
  from:
    - group: gateway.networking.k8s.io
      kind: HTTPRoute
      namespace: app-namespace
  to:
    - group: ""
      kind: Service
      name: public-api  # Only this service can be referenced

Multiple Source Namespaces¶

Allow multiple namespaces to reference Services:

apiVersion: gateway.networking.k8s.io/v1beta1
kind: ReferenceGrant
metadata:
  name: allow-multiple-namespaces
  namespace: shared-services
spec:
  from:
    - group: gateway.networking.k8s.io
      kind: HTTPRoute
      namespace: frontend
    - group: gateway.networking.k8s.io
      kind: HTTPRoute
      namespace: backend
    - group: gateway.networking.k8s.io
      kind: GRPCRoute
      namespace: grpc-apps
  to:
    - group: ""
      kind: Service

GRPCRoute Example¶

---
apiVersion: gateway.networking.k8s.io/v1beta1
kind: ReferenceGrant
metadata:
  name: allow-grpc-routes
  namespace: grpc-services
spec:
  from:
    - group: gateway.networking.k8s.io
      kind: GRPCRoute
      namespace: app-namespace
  to:
    - group: ""
      kind: Service
---
apiVersion: gateway.networking.k8s.io/v1
kind: GRPCRoute
metadata:
  name: cross-ns-grpc
  namespace: app-namespace
spec:
  parentRefs:
    - name: cloudflare-tunnel
      namespace: cloudflare-tunnel-system
  hostnames:
    - grpc.example.com
  rules:
    - matches:
        - method:
            service: mypackage.UserService
      backendRefs:
        - name: user-grpc-service
          namespace: grpc-services
          port: 50051

Status Conditions¶

When a cross-namespace reference is denied, the route status shows:

status:
  parents:
    - parentRef:
        name: cloudflare-tunnel
        namespace: cloudflare-tunnel-system
      conditions:
        - type: ResolvedRefs
          status: "False"
          reason: RefNotPermitted
          message: "Cross-namespace reference not permitted by ReferenceGrant"

Checking ReferenceGrants¶

List ReferenceGrants in a namespace:

kubectl get referencegrant --namespace backend-namespace

View details:

kubectl describe referencegrant allow-app-to-backend --namespace backend-namespace

Troubleshooting¶

RefNotPermitted Error¶

Check that:

ReferenceGrant exists in the target namespace (where Service is)
from[].namespace matches the route's namespace
from[].kind matches the route kind (HTTPRoute or GRPCRoute)
from[].group is gateway.networking.k8s.io
to[].group is "" (empty string for core API)
to[].kind is Service

Common Mistakes¶

Mistake	Fix
ReferenceGrant in wrong namespace	Create in target (Service) namespace
Wrong `from.group`	Use `gateway.networking.k8s.io`
Wrong `to.group`	Use `""` (empty string) for Services
Missing namespace in backendRef	Add explicit `namespace` field

Debug Commands¶

# Check route status
kubectl get httproute my-route --output jsonpath='{.status.parents[*].conditions}'

# Check ReferenceGrant
kubectl get referencegrant --namespace backend-namespace --output yaml

# Check controller logs
kubectl logs --selector app.kubernetes.io/name=cloudflare-tunnel-gateway-controller \
  --namespace cloudflare-tunnel-system | grep -i reference

Security Considerations¶

Least Privilege

Create ReferenceGrants with the minimum necessary permissions:

Specify exact namespaces instead of multiple entries
Use to[].name to restrict to specific Services when possible
Regularly audit ReferenceGrants in shared namespaces

Shared Namespaces

Be careful with ReferenceGrants in namespaces containing sensitive Services. A ReferenceGrant without to[].name allows access to ALL Services in that namespace.