VirtualService for gRPC not working with named port

[rfevang]

Is this a BUG or FEATURE REQUEST?:

BUG

Did you review https://istio.io/help/ and existing issues to identify if this is already solved or being worked on?: Yes

Bug:
Y

What Version of Istio and Kubernetes are you using, where did you get Istio from, Installation details

istioctl version: release-0.8-20180515-17-26
kubectl version: Server 1.9.6-gke.1, Client 1.8.6

Is Istio Auth enabled or not ?
Not

Did you install the stable istio.yaml, istio-auth.yaml.... or if using the Helm chart please provide full command line input.

Used istio.yaml

What happened:

503 when calling gRPC method exposed via gateway + virtualservice

What you expected to happen:

I expected the request to be routed to the service specified by virtualservice

How to reproduce it:

Relevant yaml definitions:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: internal-grpc
spec:
  hosts:
  - "*"
  gateways:
  - internal-grpc-gateway
  http:
  - match:
    - uri:
        prefix: /grpc.reflection.v1alpha.ServerReflection
    route:
    - destination:
        port:
#          number: 31001
          name: grpc
        host: ts-service
      weight: 100
---
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: internal-grpc-gateway
spec:
  selector:
    istio: ingressgateway
  servers:
  - hosts:
    - "*"
    port:
      number: 80
      protocol: grpc
---
apiVersion: v1
kind: Service
metadata:
  name: ts-service
  labels:
    interface: grpc
    environment: test
spec:
  selector:
    app: ts-server
  ports:
    - name: grpc
      port: 31001
      targetPort: grpc

Note that commenting out the name: grpc line and uncommenting the number: 31001 line makes this work correctly.

[xiajidexue]

Any progresses?