I'm trying to patch an Istio's RouteRule on the fly by changing the proportion of traffic each version of the service receives. Right now when I run

kubectl describe routerule my-rule

I get the description:

Name:         my-rule
Namespace:    default
Labels:       <none>
Annotations:  kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"config.istio.io/v1alpha2","kind":"RouteRule","metadata":{"annotations":{},"name":"my-rule","namespace":"default"},"spec":...
API Version:  config.istio.io/v1alpha2
Kind:         RouteRule
Metadata:
  Cluster Name:        
  Creation Timestamp:  2018-05-25T16:21:59Z
  Generation:          0
  Resource Version:    154906
  Self Link:           /apis/config.istio.io/v1alpha2/namespaces/default/routerules/my-rule
  UID:                 bfd78178-6037-11e8-8d5c-06f2e5b7e6b2
Spec:
  Destination:
    Name:  MyApp
  Match:
    Request:
      Headers:
        Uri:
          Prefix:  /MyApp/
  Rewrite:
    Uri:  /
  Route:
    Labels:
      Version:  v1
    Weight:     10
    Labels:
      Version:  v2
    Weight:     90

Now I want to change the rule such that 90% of traffic is sent to v1 and 10% to v2:

kubectl patch routerule my-rule --type='json' -p='[{"op":"replace", "path":"/spec/route", "value":[{"labels":{"version":"v1"}, "weight": "90"}, {"labels":{"version":"v2"}, "weight": "10"}]}]'

When I run this, the command succeeds with routerule.config.istio.io "my-rule" patched; and if I run kubectl describe on my rule again I can verify it has the updated values:

...
Route:
Labels:
  Version:  v1
Weight:     90
Labels:
  Version:  v2
Weight:     10

However, this doesn't actually take effect. When I hit the endpoint, I still see the original rules are applied (most of the traffic is sent to v2). Any ideas as to what could be causing this? Do I need to somehow inform Istio that the rule has changed?