While you might have used REST as your service communications layer in the past, more and more projects are moving to an event-driven architecture. When a service performs some piece of work that other services might be interested in, that service produces an event — a record of the performed action. Other services consume those events so that they can perform any of their own tasks needed as a result of the event.
Since version 3.0, event-based communication is the framework prime focus of interest. It defines a uniform interface for asynchronous processing of incoming events. The mental model is very similar to other popular libraries that you can find in the frontend, like —
ngrx/effects. Both libraries had a huge influence on design and architectural decisions.