Messaging Patterns with Akka (Remote) Actors

John Nestor and Dragos Manolescu Whitepages, Inc.

April 14, 2015

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

Akka Remote Actors• Design decisions:

• Symmetric communication

• Symmetric roles

• Remote scenarios:

• Lookup

• Remote creation

Akka Actor Model

Actor

BehaviorMailbox

Parent

Child

Child

M M M

Actor

BehaviorMailbox

Messages

- Configuration- Thread pools

Actor System

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

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 } } }

Messaging Pattern: OneWay

Client Actor

Server Actor

JSON(cmd, id, msg)

(server work)

Messaging Pattern: Request-Reply

Client Actor

Server Actor

JSON(cmd, id, msg)

(server work)

JSON("done", id, msg)

Messaging Pattern: Request-Reply with Failure

Client Actor

Server Actor

JSON(cmd, id, msg)

(server work)

JSON("fail", id, msg)

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

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)

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

Messaging Pattern: Long Polling

Client Actor

Server Actor

(server work)

JSON("StopListen", id, msg)

JSON

JSON("StartListen", id, msg)

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!

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

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

Thank you