Define an Istio VirtualService and DestinationRule to implement header-based traffic routing between two versions of a service for A/B testing

Steps

1. Label the two Deployment versions with app: myservice and version: v1 / version: v2 respectively to allow Istio subsets to select them
2. Create a DestinationRule that defines subsets: name: v1 with labels: version: v1 and name: v2 with labels: version: v2; set trafficPolicy if needed for connection pool settings
3. Create a VirtualService with hosts: [myservice] and an http route list: place the header-match rule first — match: [{headers: {x-variant: {exact: v2}}}] routed to subset v2, followed by a catch-all route to subset v1
4. Apply both resources: kubectl apply -f destinationrule.yaml -f virtualservice.yaml and verify with istioctl analyze to catch misconfiguration
5. Test routing by sending requests with the header: curl -H 'x-variant: v2' http://myservice/ and confirming the v2 pod handles it via pod logs or Kiali traffic graph
6. Monitor with istioctl dashboard kiali or by querying Prometheus for istio_requests_total labeled by destination_version to confirm traffic split is working as expected