Is there an example of sending messages between actors using "Akkling.Cluster.Sharding"?

Question

This may be a duplicate.

Thus, I have made some progress. However, I find it challenging to interpret the reference documentation from the C# API to the desired Akka.FSharp API.

As of now, I am only able to send messages from my client program and not an actor.

let consumer (actor:Actor<_>) msg = 
    printfn "\n%A received %A" (actor.Self.Path.ToStringWithAddress()) (box msg) |> string |> ignored

let system1 = System.create "cluster-system" (configurePort 2551)
let shardRegion1 = spawnSharded id system1 "printer" <| props (actorOf2 consumer)

shardRegion1 <! ("shard-1", "entity-1", "hello world 1")

The code above works. However, it only works with strings as messages. I am still struggling to get actors to send messages to each other with various typed messages.

NOTE:

I got the Akka.Persistence.SqlServer plugin working.

However, I am not clear on how to retrofit the following setup within Akkling.Cluster.Sharding:

open Akka.FSharp
let clusterHostActor =
    spawn system1 nodeName <| fun (inbox: Actor<_>) -> 
        let cluster = Cluster.Get system1
        cluster.Subscribe(inbox.Self, [| typeof<ClusterEvent.IClusterDomainEvent> |])
        inbox.Defer(fun () -> cluster.Unsubscribe(inbox.Self))
        let rec messageLoop () = 
            actor {
                let! message = inbox.Receive()                        
                match box message with
                | :? ClusterEvent.MemberUp      as event -> printfn "Member %s Joined the Cluster at %O" event.Member.Address.Host DateTime.Now
                                                            let sref = select (event.Member.Address.ToString() + "/user/listener") inbox
                                                            sref <! "Hello from clusterHostActor"
                | :? ClusterEvent.MemberRemoved as event -> printfn "Member %s Left the Cluster at %O"   event.Member.Address.Host DateTime.Now
                | other ->                                  printfn "Cluster Received event %O at %O" other DateTime.Now

                return! messageLoop()
            }
        messageLoop()

Specifically, I was under the impression that a shard-region is required within a sharded cluster system in order to send messages back and forth between actors.

As someone that is new to this paradigm, I am struggling to create a simple "hello world" type messaging program between two actors using the sharding functionality.

Any suggestions?

score 1 · Answer 1 · edited Mar 17 '17 at 16:50

If you want for your shard node to be valid host/container for sharded actors, it must be running shard region associated with that type of an actor. All messages sent to sharded actors are sent through a shardRegion reference.

In the first example snippet, you've shown that, string messages are the only valid message types probably because your consumer behavior takes a string as the only valid message type.

As you may see in spawnSharded definition, it takes 4 parameters. What matters here is the first one, which is a function that is used to resolve all of the info required by the sharding plugin in order to route the message to a valid actor/entity. This method returns a tuple where:

First element is an identifier of shard, target entity lives in.
Second element is an identifier of entity itself in scope of its shard. So, to uniquely identify entity among all other entities within a cluster, it must provide a unique shard-id/entity-id pair.
Third parameter is an actual message, that is going to be sent to an entity. Its type should match the type of a recursive loop function input used as your actor behavior - in case you've shown, it would probably be a plain object.

Since in the example, this message resolver function is id (identity), we send a tuple directly to shard region. You may change that function to whatever else you want to specify something custom.

PS: if you have more questions, an Akka.NET gitter channel is the place when you can find help.

Is there an example of sending messages between actors using "Akkling.Cluster.Sharding"?

1 Answers1