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Virtual services,along with destination rules, are the key building blocks of Istio’s trafficrouting functionality. A virtual service lets you configure how requests arerouted to a service within an Istio service mesh, building on the basicconnectivity and discovery provided by Istio and your platform. Each virtualservice consists of a set of routing rules that are evaluated in order, lettingIstio match each given request to the virtual service to a specific realdestination within the mesh. Your mesh can require multiple virtual services ornone depending on your use case. Virtual services play a key role in making Istio’s traffic management flexibleand powerful. They do this by strongly decoupling where clients send theirrequests from the destination workloads that actually implement them. Virtualservices also provide a rich way of specifying different traffic routing rulesfor sending traffic to those workloads. Why is this so useful? Without virtual services, Envoy distributestraffic using round- robin load balancing between all service instances, asdescribed in the introduction. You can improve this behavior with what you knowabout the workloads. For example, some might represent a different version. Thiscan be useful in A/B testing, where you might want to configure traffic routesbased on percentages across different service versions, or to directtraffic from your internal users to a particular set of instances. With a virtual service, you can specify traffic behavior for one or more hostnames.You use routing rules in the virtual service that tell Envoy how to send thevirtual service’s traffic to appropriate destinations. Route destinations canbe versions of the same service or entirely different services. A typical use case is to send traffic to different versions of a service,specified as service subsets. Clients send requests to the virtual service host as ifit was a V