If I enable Istio on some of my apps (but not all of them) using Manual sidecar injection, can I route traffic between non-based-Istio apps and Istio-based apps? If yes, is it still true if I enable Citadel? I'm wondering because I'd like to slowly enable the sidecar injection on my apps and migrate over. Do both Istio-based-apps and non-Istio-based apps still talk to each other (within cluster) via the normal Kubernetes service objects? Is there anything else I need to do in order to allow Istio and regular services to talk to each other?

I'm new to Istio, so any context is helpful.