A handful of messaging patterns distilled from work with Akka remote actors in Scala

1. Messaging Patterns with
Akka (Remote) Actors
John Nestor and Dragos Manolescu
Whitepages, Inc.
April 14, 2015

2. Prelude
• JLine (http://jline.sourceforge.net)
• Command history, tab completion, line editing
• Custom key bindings
• PersistJson (https://github.com/nestorpersist/json)
• Fast Scala JSON parser
• JSON tree/Scala classes
• Pretty/Compact
• Demo code at https://github.com/polymorphic/akka-messaging-
patterns.git

3. Akka Remote Actors
• Design decisions:
• Symmetric communication
• Symmetric roles
• Remote scenarios:
• Lookup
• Remote creation

4. Akka Actor Model
Actor
BehaviorMailbox
Parent
Child
Child
M M M
Actor
BehaviorMailbox
Messages
- Configuration
- Thread pools
Actor System

5. Akka Actor Model w/
Remoting
Actor
BehaviorMailbox
Parent
Child
Child
M M MActor
BehaviorMailbox
Messages
- Configuration
- Thread pools
Actor System
Lookup via ActorSelection
Remote creation via deployment configuration
- Configuration
- Thread pools
Actor System

6. Actor System Configuration
for Remoting
akka {
actor {
provider = "akka.remote.RemoteActorRefProvider"
}
remote {
enabled-transports = ["akka.remote.netty.tcp"]
netty.tcp {
hostname = "127.0.0.1"
port = 2552
}
}
}

7. Messaging Pattern:
OneWay
Client Actor
Server Actor
JSON(cmd, id, msg)
(server work)

8. Messaging Pattern:
Request-Reply
Client Actor
Server Actor
JSON(cmd, id, msg)
(server work)
JSON("done", id, msg)

9. Messaging Pattern:
Request-Reply with Failure
Client Actor
Server Actor
JSON(cmd, id, msg)
(server work)
JSON("fail", id, msg)

10. Messaging Pattern:
Request-Reply with Ack
Client Actor
Server Actor
(server work)
JSON("done", id, msg)
JSON(cmd, id, msg)
JSON("ack", id, msg)
Timer

11. Messaging Pattern:
Request-Reply with Progress
Client Actor
Server Actor
(server work)
JSON("done", id, msg)
JSON(cmd, id, msg)
(server work)
(server work)
(server work)
JSON("progress", id, msg)
JSON("progress", id, msg)
JSON("progress", id, msg)

12. Messaging Pattern:
Request-Reply with Query
Client Actor
Server Actor
(server work)
JSON(cmd, id, msg)
(user input)
(server work)
JSON("query", id, msg)
JSON
(server work)
JSON("done", id, msg)
Repeat 2x

13. Messaging Pattern:
Long Polling
Client Actor
Server Actor
(server work)
JSON("StopListen", id, msg)
JSON
JSON("StartListen", id, msg)

14. Messaging Patterns
• More patterns:
• Sender retries on timeout or failure
• A -> B, B -> C, C responds to A directly
• Routers
• Suggestions for more patterns welcome!

15. Summary:
Remote Actors or HTTP?
• Remote actors:
• Symmetric; uniform for local/remote
• Rich interaction patterns, very simple protocol
• Problems with NAT and load balancers
• HTTP:
• Asymmetric; remote-only
• Simple interaction patterns, complex protocol
• Ubiquitous
• Originally designed for a very different purpose

16. For More Information
• Sample code: https://github.com/polymorphic/akka-
messaging-patterns.git
• Akka remoting: http://doc.akka.io/docs/akka/2.3.9/
scala/remoting.html
• JLine http://jline.sourceforge.net
• PersistJson https://github.com/nestorpersist/json
• Effective Akka, Patterns and Best Practices by Jamie
Allen

17. Thank you