My project is a set of nodes. Each node is an actor. A user can view a set of nodes (in a web page). Each node can have its state updated independent of user action.
(For instance, a user A might only be viewing nodes 2-4. Node 1 could receive a message from a different user. Node 1 would then propagate the message, through actor messages, resulting in state changes to nodes 3 and 4. User A should see those changes to 3 and 4.)
I want the user to see the accurate state of the node as it changes. Therefore, I want the server to transmit events to the client when these node state changes occur.
I was thinking I’d use Server Sent Events (SSE). When a user/client connects, it would indicate which set of nodes it is viewing. When the user/client changes which set of nodes it is viewing, it would communicate that to the backend; dropping some and adding others. The SSE connection would transmit state changes for all the nodes that the user/client is currently viewing.
I know how to set up the route thanks to https://doc.akka.io/docs/akka-http/10.0/sse-support.html .
I am wondering the best way to communicate the actor state changes to the route?
I am using akka cluster sharding and persistence on Akka 2.5 currently, but will update to 2.6 at some point. Each actor is identified by a uuid.
It sounds like I should use one EventBus across the entire cluster? And then any time an actor’s state changes, it would
eventBus.publish(Msg(uuid, state)) ?
It sounds like EventStream is not an option since I am using Cluster. Is that also true for EventBus in general? Should I be looking to Distributed Pub/Sub or an external message queue/stream instead?
Finally, either way, is there an example of hooking that up to SSE in the akka-http route? Is this mostly a matter of creating some sort of listener actor for that “view” of nodes that the user cares about, and then somehow hooking that up to the
Source that SSE needs?