Is there a way to prevent a VirtualService from routing to empty/unhealthy destinations?
For example, consider the following VirtualService and DestinationRule:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: httpy
spec:
  hosts:
    - httpy
  http:
    - route:
      - destination:
          host: httpy
          subset: prod
        weight: 90
      - destination:
          host: httpy
          subset: canary
        weight: 10
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: httpy
spec:
  host: httpy
  subsets:
  - name: prod
    labels:
      isCanary: "false"
  - name: canary
    labels:
      isCanary: "true"

Imagine that there are no healthy pods in the httpy service that have the isCanary: "true" label either because A) zero pods have the isCanary: "true" label or B) all of the canary pods are unready/unhealthy. This will result in 10% of requests to the httpy returning a "no healthy upstream" response.

Is there a good way to avoid this? Is it possible to make the VirtualService "smarter" and have it not route traffic to an obviously unusable destination?

If you want to try this out yourself, apply the following gist then delete the httpy-canary deployment: https://gist.github.com/llamasoft/aaca58fda0ec2e06f2fee4f272691460