High level view on the basics of Akka

1. Introduction to
Akka
Actor Framework

2. Akka – an actor framework
A
B
C
D
X
Actor system:
• An object model composed
of actors
• Communication by
asynchronous message
passing
• Message delivery (in
general) not guaranteed
• Java & Scala API
Microservices in one app
E

3. An actor
• Reacts to messages
• Is a ‘living’ object
• Has a:
o Name
o Location
o Mutable state
o Lifecycle
o A mailbox
o A parent
o Optionally, children
o Changeable behavior
A
Props
ActorRef
Internally synchronous!

4. Actor hierarchy
A
B
C
D
X
• Actors form a supervision tree
• A child’s life is governed by its
parent
• Failure handling is
independent from cause
• Failure is local
• Failure will happen…
E

5. What does it all give?
 Actors are independent processing cells
 It’s fast, non blocking
 It gives a horizontally scalable application architecture
 Composes well with regular objects

6. Log sources
The problem to crunch – log processing
File
Single line
Json
LogAggregatorLogReceiver Json
LogReceiverService

7. Log sources
Possible Architecture
File
Single line
Json
LogAggregatorLogReceiver
Single Line
Processor
Single Line
Multiline
Processor
Multiple lines
Single Line
Json
Json

8. Log sources
Another possibility
File
Single line
Json
LogAggregatorLogReceiver
Single Line
Processor
Single Line
Multiline
Processor
Multiple lines
Single Line
Json
Json
Json

9. Log sources
Another one – concepts changed
File
Single line
Json
LogAggregatorLogReceiver
Line
Parser
Single Line
LogProcessor
Multiple lines
Single Line
Json
Json
Json

10. Actor lifecycle
A
Restart
Start
Stop
PoisonPill
Exception
Supervised by actor’s parent
• Stop the child?
• Restart the child?
• Restart all children?
• Escalate (throw to parent)?

11. Old-school web application vs actor hierarchy
Controller
ServiceC
ServiceB
DAO
ServiceD
Stateless
Static
A
B
C
D
X
E
Stateful
Dynamic

12. A
B
C
The internals
Thread
Thread
Thread
ExecutionContextDispatcher
Future Future
• Fork-Join Pool
• Threadpool

13. Best practices
• Think of the hierarchy up-front
• Avoid singleton root actors
• Use ActorRefs, avoid the slow ActorSelection
• Always be prepared for failure => use timeouts
• Use context.become to separate behavior by states
• Monitor, log, measure everything
• Don’t optimize the performance (yet)
• If you can, delegate it => ensure single responsibility

14. Readings
• http://doc.akka.io/docs/akka/2.3.7/scala.html
• http://letitcrash.com/
• Akka Concurency
• Akka in Depth
• Akka in Action - MEAP
• Functional and Reactive Domain Modeling – MEAP
• Code samples via Activator