Question

I want to build an actor system that has a common server at a static IP address and port. There will be many clients that know the server’s address. The server doesn’t know the IP addresses of the clients.

Configuration of the server:

akka {
  actor {
    provider = "akka.remote.RemoteActorRefProvider"
  }
  remote {
    transport = "akka.remote.netty.NettyRemoteTransport"
    netty {
      hostname = "46.38.232.161"
      port = 2552
    }
  }
}

Configuration of the client:

akka {
  actor {
    provider = "akka.remote.RemoteActorRefProvider"
  }
  remote {
    transport = "akka.remote.netty.NettyRemoteTransport"
    netty {
      port = 2553
    }
  }
}

A client may come from the entire internet. Now I want to send messages from actors on the client to actors on the server. How does the server know, where to send back his messages? When I send ActorPaths to the server, so he would know the corresponding client’s address, these don’t contain the client’s IP address.

Answer 1

akka.remote.netty.hostname property may be set inside your application.conf, to a reachable IP address or resolvable name, in a case you want to communicate across the network. Actually your “client” nodes will also be a servers, when using Akka.

In a case if address is unknown at app start, consider this code fragment from Akka documentation:

import akka.actor.ActorSystem
import com.typesafe.config.ConfigFactory

val customConf = ConfigFactory.parseString("""
  akka.actor.deployment {
    /my-service {
      router = round-robin
      nr-of-instances = 3
    }
  }
""")

// ConfigFactory.load sandwiches customConfig between default reference
// config and default overrides, and then resolves it.
val system = ActorSystem("MySystem", ConfigFactory.load(customConf))