<p>I have a monolithic application that is being broken down into domains that are microservices. The microservices live inside a kubernetes cluster using the istio service mesh. I'd like to start replacing the service components of the monolith little by little. Given the UI code is also running inside the cluster, microservices are inside the cluster, but the older web api is outside the cluster, is it possible to use a VirtualService to handle paths I specify to a service within the cluster, but then to forward or proxy the rest of the calls outside the cluster?</p>
<p><a href="https://i.stack.imgur.com/MF03C.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MF03C.png" alt="enter image description here" /></a></p>

<p>You will have to define a ServiceEntry so Istio will be aware of your external service. That ServiceEntry can be used as a destination in a VirtualService. <a href="https://istio.io/latest/docs/reference/config/networking/virtual-service/#Destination" rel="nofollow noreferrer">https://istio.io/latest/docs/reference/config/networking/virtual-service/#Destination</a></p>
