Istio Subset-level traffic splitting removes other DestinationRoutes

[dnguy078]

Checklist:

• I've included steps to reproduce the bug.
• I've included the version of argo rollouts.

Describe the bug

• Argo Rollouts removes any subset level DestinationRoutes in a VirtualService that it not modifying during a Canary Rollout.
• I have a VirtualService where I want to route a certain percentage to a newer system while maintaining a canary release for a legacy service.
• In the following case below, Argo Rollouts will remove the DestinationRoutes with host rollout-alpha-example following a rollout. Ideally, I'd also want the flexibility to define a maxWeight in which Rollouts would setWeight up to the maxWeight for a HTTP DestinationRoute.

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: istio-gateway
  labels:
    app: istio-gateway
spec:
  selector:
    istio: ingressgateway
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - "*"
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: rollout-vsvc
spec:
  gateways:
  - istio-rollout-gateway
  http:
  - match:
    - uri:
        prefix: "/somepath"
  - name: primary
    route:
    - destination:
        host: rollout-example
        subset: stable
      weight: 100
    - destination:
        host: rollout-example
        subset: canary
      weight: 0
    - destination:
        host: rollout-alpha-example
        subset: stable1
      weight: 20
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: rollout-destrule
spec:
  host: rollout-example
  subsets:
  - name: canary
    labels:
      app: rollout-example
  - name: stable
    labels:
      app: rollout-example
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: rollout-alpha-destrule
spec:
  host: rollout-alpha-example
  subsets:
  - name: stable1
    labels:
      app: rollout-alpha-example

Rollout.yaml

---
apiVersion: argoproj.io/v1alpha1
kind: Rollout
metadata:
  name: rollout-example
  labels:
    app: rollout-example
spec:
  strategy:
    canary:
      trafficRouting:
        istio:
          virtualService:
            name: rollout-vsvc  
            routes:
            - primary  
          destinationRule:
            name: rollout-destrule  
            canarySubsetName: canary 
            stableSubsetName: stable
      steps:
        - setWeight: 50
        - pause: { duration: 10 }

  replicas: 4
  revisionHistoryLimit: 2
  selector:
    matchLabels:
      app: rollout-example
  template:
    metadata:
      labels:
        app: rollout-example
    spec:
      containers:
      - name: demo
        image: argoproj/rollouts-demo:blue
        imagePullPolicy: Always
        ports:
        - name: web
          containerPort: 8080
        resources:
          requests:
            memory: "64Mi"
            cpu: "100m"
          limits:
            memory: "128Mi"
            cpu: "140m"
---
apiVersion: v1
kind: Service
metadata:
  name: rollout-example
spec:
  ports:
  - port: 80
    targetPort: http
    protocol: TCP
    name: http
  selector:
    app: rollout-example

To Reproduce

• Create above resources
• kubectl argo rollouts set image rollout-example "*=argoproj/rollouts-demo:yellow"
• Observe Argo Rollouts remove virtual service's destinationRoute rollout-alpha-example

Expected behavior

• Argo Rollouts should not modify any other DestinationRoute not defined by spec.strategy.trafficRouting.istio.destinationRule.name

Screenshots

Version
v1.6.0

Logs

INFO[0022] Reconciling TrafficRouting with type 'Istio'  namespace=default rollout=rollout-example
INFO[0022] VirtualService `rollout-vsvc` set to desiredWeight '100'  event_reason="Updated VirtualService" namespace=default rollout=rollout-example
INFO[0022] Previous weights: &TrafficWeights{Canary:WeightDestination{Weight:50,ServiceName:,PodTemplateHash:77c794f4c8,},Stable:WeightDestination{Weight:50,ServiceName:,PodTemplateHash:5f6685b4fd,},Additional:[]WeightDestination{},Verified:nil,}  namespace=default rollout=rollout-example
INFO[0022] New weights: &TrafficWeights{Canary:WeightDestination{Weight:100,ServiceName:,PodTemplateHash:77c794f4c8,},Stable:WeightDestination{Weight:0,ServiceName:,PodTemplateHash:5f6685b4fd,},Additional:[]WeightDestination{},Verified:nil,}  namespace=default rollout=rollout-example
INFO[0022] Event(v1.ObjectReference{Kind:"Rollout", Namespace:"default", Name:"rollout-example", UID:"423d8966-fd28-4b7e-98ae-4bdfd48a55ec", APIVersion:"argoproj.io/v1alpha1", ResourceVersion:"2774866", FieldPath:""}): type: 'Normal' reason: 'Updated VirtualService' VirtualService `rollout-vsvc` set to desiredWeight '100'
INFO[0022] Traffic weight updated from 50 to 100         event_reason=TrafficWeightUpdated namespace=default rollout=rollout-example
INFO[0022] No Steps remain in the canary steps           namespace=default rollout=rollout-example
INFO[0022] Event(v1.ObjectReference{Kind:"Rollout", Namespace:"default", Name:"rollout-example", UID:"423d8966-fd28-4b7e-98ae-4bdfd48a55ec", APIVersion:"argoproj.io/v1alpha1", ResourceVersion:"2774866", FieldPath:""}): type: 'Normal' reason: 'TrafficWeightUpdated' Traffic weight updated from 50 to 100
INFO[0022] Event(v1.ObjectReference{Kind:"Rollout", Namespace:"default", Name:"rollout-example", UID:"423d8966-fd28-4b7e-98ae-4bdfd48a55ec", APIVersion:"argoproj.io/v1alpha1", ResourceVersion:"2774866", FieldPath:""}): type: 'Normal' reason: 'RolloutCompleted' Rollout completed update to revision 5 (77c794f4c8): Completed all 2 canary steps
INFO[0022] Rollout completed update to revision 5 (77c794f4c8): Completed all 2 canary steps  event_reason=RolloutCompleted namespace=default rollout=rollout-example
INFO[0022] Patched: {"status":{"availableReplicas":8,"canary":{"weights":{"canary":{"weight":100},"stable":{"weight":0}}},"conditions":[{"lastTransitionTime":"2023-10-24T16:44:58Z","lastUpdateTime":"2023-10-24T16:44:58Z","message":"Rollout has minimum availability","reason":"AvailableReason","status":"True","type":"Available"},{"lastTransitionTime":"2023-10-25T17:43:39Z","lastUpdateTime":"2023-10-25T17:43:39Z","message":"Rollout is not healthy","reason":"RolloutHealthy","status":"False","type":"Healthy"},{"lastTransitionTime":"2023-10-25T17:44:28Z","lastUpdateTime":"2023-10-25T17:44:28Z","message":"Rollout is paused","reason":"RolloutPaused","status":"False","type":"Paused"},{"lastTransitionTime":"2023-10-25T17:44:28Z","lastUpdateTime":"2023-10-25T17:44:32Z","message":"ReplicaSet \"rollout-example-77c794f4c8\" is progressing.","reason":"ReplicaSetUpdated","status":"True","type":"Progressing"},{"lastTransitionTime":"2023-10-25T17:44:32Z","lastUpdateTime":"2023-10-25T17:44:32Z","message":"RolloutCompleted","reason":"RolloutCompleted","status":"True","type":"Completed"}],"message":null,"phase":"Healthy","readyReplicas":8,"stableRS":"77c794f4c8"}}  generation=5 namespace=default resourceVersion=2774866 rollout=rollout-example
INFO[0022] persisted to informer                         generation=5 namespace=default resourceVersion=2774876 rollout=rollout-example
INFO[0022] Reconciliation completed                      generation=5 namespace=default resourceVersion=2774866 rollout=rollout-example time_ms=16.033625

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