Akka Actor internal state during shard migration in a cluster

Question

we are using Akka sharding to distribute our running actors across several Nodes. Those actors are Persistent and we keep their internal state in the database.

Now we need to add ActorRef to "metrics actor", running on each node. Each actor in shard is supposed to send telemetric data to metrics actor - it must choose the right metrics actor which is running locally on the very same node. Reason is, Metric actor gathers data peer node.

Now, I was just thinking to create Metric actor in Main method (which runs initially on each node):

val mvMetrics : ActorRef = system.actorOf(MetricsActor("mv"), "mvMetrics")

and then pass that reference to ClusterSharding inicialisation as a part of Actors props object:

    ClusterSharding(system).start(
        typeName = shardName,
        entityProps = MyShardActor.props(mvMetrics),
        settings = ClusterShardingSettings(system),
        extractEntityId = idExtractor,
        extractShardId = shardResolver)

My question is, what happen if such created actors migrate between nodes, e.g. from Node A -> B? I can imagine that migrated props object on node B remains the same as on node A, so the ActorRef remains the same and therefore newly created actor will be sending metrics data to original node A?

Thanks

Reza Reza · Accepted Answer · 2016-07-12T05:19:06

How about taking advantage of ActorRef.path? imagine that each node has its actor named in a certain way, and then an actor will dynamically find the relevant metrics actor using the path.

Akka Actor internal state during shard migration in a cluster

1 Answers