istiod vs istio pilot

Istio’s control plane is, itself, a modern, cloud-native application. Thus, it was built from the start as a set of microservices. Individual Istio components like service discovery (Pilot), configuration (Galley), certificate generation (Citadel) and extensibility (Mixer) were all written and deployed as separate microservices. The need for these components to communicate securely and be observable, provided opportunities for Istio to eat its own dogfood (or “drink its own champagne”, to use a more French version of the metaphor!).

[…] in Istio 1.5, we’ve changed how Istio is packaged, consolidating the control plane functionality into a single binary called istiod.

https://istio.io/latest/blog/2020/istiod/