Actor concurrency, consistency, and lifetime

The Dapr actor model relies on two main components: the Dapr runtime, operating in the sidecar, and the Dapr placement service. We’ll understand each of these in the following sections.

Placement service

The placement service is responsible for keeping a map of the Dapr instances that are capable of serving actors. Considering our example, the reservationactor-service application is an example of such a service.

Once a new instance of our new reservationactor-service Dapr application starts, it informs the placement service that it is ready to serve actors of the ReservationItemActor type.

The placement service broadcasts a map – in the form of a hash table with the host’s information and the served actor types – to all the Dapr sidecars operating in the environment.

Thanks to the host’s map being constantly updated, actors are uniformly distributed over the actor service instances.

In...