I have a problem with Istio Request Routing directly behind the Istio Ingress Gateway:

I have simple node.js app (web-api) in 2 versions (v1, v2) with an Istio Ingress Gateway directly in frontand an Istio VirtualService that is supposed to do a 80/20 distribution between version 1 and 2 but it doesn't. Kiali shows a 50/50 distribution.

When I add a simple frontend service that just passes the request through, everything works as expected. According to the Istio documentation using an Istio ingress allows for request routing rules in user-facing services. But for me it doesn't and I don't understand why?

deployment.yaml:

apiVersion: apps/v1beta2 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: web-api-v1
spec:
  selector:
    matchLabels:
      app: web-api
      project: istio-test
      version: v1
  replicas: 1
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: web-api
        project: istio-test
        version: v1
    spec:
      containers:
      - image: web-api:1
        name: web-api-v1
        env:
        - name: VERS
          value: "=> Version 1"
        ports:
        - containerPort: 3000
          name: http
      restartPolicy: Always    
---
apiVersion: apps/v1beta2 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: web-api-v2
spec:
  selector:
    matchLabels:
      app: web-api
      project: istio-test
      version: v2
  replicas: 1
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: web-api
        project: istio-test
        version: v2
    spec:
      containers:
      - image: web-api:1
        name: web-api-v1
        env:
        - name: VERS
          value: "=> Version 2"
        ports:
        - containerPort: 3000
          name: http
      restartPolicy: Always    
---

service.yaml

apiVersion: v1
kind: Service
metadata:
  name: web-api
  labels:
    app: web-api
    project: istio-test
spec:
  type: NodePort
  ports:
    - port: 3000  
      name: http
      protocol: TCP
  selector:
    app: web-api
---

istio-ingress.yaml:

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: default-gateway-ingress
spec:
  selector:
    istio: ingressgateway # use Istio default gateway implementation
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - "*"
--- 
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: virtualservice-ingress
spec:
  hosts:
  - "*"
  gateways:
  - default-gateway-ingress
  http:
  - match:
    - uri:
        exact: /test
    route:
    - destination:
        host: web-api
        port:
          number: 3000
--- 

istio-virtualservice.yaml:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: web-api
spec:
  hosts:
  - web-api
  http:
  - route:
    - destination:
        host: web-api
        subset: v1
      weight: 80  
    - destination:
        host: web-api
        subset: v2 
      weight: 20   
---

I have put this example on https://github.com/Harald-U/istio-test