What is the purpose of VirtualService in Istio?

VirtualService in Istio is used to define traffic routing rules within the service mesh. It allows flexible management of how requests are directed to different versions of services, implementing canary releases, A/B testing, load balancing, and error handling.

For example, with VirtualService, you can configure 90% of traffic to go to the stable version of a service, and 10% to a new, test version:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: my-service
spec:
  hosts:
  - my-service
  http:
  - route:
    - destination:
        host: my-service
        subset: stable
      weight: 90
    - destination:
        host: my-service
        subset: canary
      weight: 10

Thus, VirtualService is a key object for managing network traffic behavior in Istio.