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Scaling up & out - with Actors
√
Akka Tech Lead
Email: [email protected]
Twitter: @viktorklang
Saturday, March 10, 12
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2.0
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Akka (Áhkká):
The name comes from the goddess in the Sami
mythology that represented all the wisdom and
beauty in the world.
It is also the name of a beautiful mountain in
Laponia in the north part of Sweden
2.0
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View from the summit
2.0
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The problem
It is way too hard to build
‣ correct highly concurrent systems
‣ truly scalable systems
‣ self-healing, fault-tolerant systems
...using “state-of-the-art” tools
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Concurrency
Scalability
Fault-tolerance
…made Simpler
Vision
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Manage system overload
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Scaling: up & out
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Replicate and distribute
for fault-tolerance
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Transparent load balancing
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Markets Use cases
FINANCE & BANKING
BETTING & GAMING
TELECOM & TV
E-COMMERCE
SIMULATION
SOCIAL
• Event-driven messaging systems
• Stock trend Analysis & Simulation
• Streaming media network gateways
• Massive multiplayer online gaming
• High throughput and transactional
betting
• 3D simulation engines
• Social media community sites
Applicability
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Akka 2.0
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Design for distribution
–
In-VM is an optimization
opportunity
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Async at heart
–
Even for control
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CAS is mother,
CAS is father.
–
No locks in hot path
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Fault-tolerance as default
–
Enforced parental
supervision
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Always room for
improvement
–
Simplify, Refactor, Replace
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A simple version
bump?
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700 tickets closed
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1020 files changed
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98683 lines added
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57415 lines removed
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Scale up
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Akka Actors
one tool in the toolbox
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Behavior
State
Actor
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Event-
driven
Behavior
State
Actor
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Event-
driven
Behavior
State
Actor
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Event-
driven
Behavior
State
Actor
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Event-
driven
Behavior
State
Actor
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Event-
driven
Behavior
State
Actor
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Behavior
State
Actor
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Event-
driven
Behavior
State
Actor
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import akka.actor.ActorSystem
import com.typesafe.config.ConfigFactory
val system =
ActorSystem(
“my-app-name”,
ConfigFactory.load(“application”)
)
Create Application
Scala API
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case object Tick
class Counter extends Actor {
var counter = 0
def receive = {
case Tick =>
counter += 1
println(counter)
}
}
Actors
Scala API
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val counter = system.actorOf(Props[Counter])
Create Actors
counter is an ActorRef
Creates a top-level actor
Scala API
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system stop actorRef
Stop actors
...also stops all actors in the hierarchy below
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counter ! Tick
Send: !
Scala API
fire-forget
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counter tell Tick
counter.tell(Tick, sender)
...or use tell
fire-forget
Scala API
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import akka.patterns.ask
implicit val timeout = Timeout(5 seconds)
val f = actor ? message
Send: ?
returns a Future[Any]
Scala API
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import akka.patterns.ask
val future =
ask(actor, message, 5 seconds)
Send: ?
returns a Future[Any]
Scala API
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class SomeActor extends Actor {
def receive = {
case User(name) =>
// reply to sender
sender ! (“Hi ” + name)
}
}
Reply
Scala API
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become
context become {
// new body
case NewMessage =>
...
}
Scala API
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unbecome
context.unbecome()
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Routers
‣ RoundRobin
‣ Random
‣ SmallestMailbox
‣ Broadcast
‣ ScatterGatherFirstCompleted
… Custom
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Routers
val router =
system.actorOf(
Props[SomeActor].withRouter(
RoundRobinRouter(nrOfInstances = 5)))
Scala API
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Router + Resizer
val resizer = DefaultResizer(lowerBound = 2,
upperBound = 15)
val router =
system.actorOf(
Props[ExampleActor1].withRouter(
RoundRobinRouter(resizer = Some(resizer))
)
)
Scala API
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Scale up?
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ThreadPoolExecutor
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ThreadPoolExecutor
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new ForkJoinPool
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new ForkJoinPool
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~2.7m actors/GB
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Let it crash
fault-tolerance
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Which components have
critically important state
and
explicit error handling?
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Fault-tolerant
onion-layered
Error Kernel
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Error
Kernel
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Error
Kernel
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Error
Kernel
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Error
Kernel
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Error
Kernel
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// from within an actor
val child = context.actorOf(Props[MyActor], “my-actor”)
Parental automatic supervision
Scala API
transparent and automatic fault handling by design
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Guardian System Actor
Parental automatic supervision
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Guardian System Actor
Parental automatic supervision
system.actorOf(Props[Foo], “Foo”)
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Foo
Guardian System Actor
Parental automatic supervision
system.actorOf(Props[Foo], “Foo”)
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Foo
Guardian System Actor
Parental automatic supervision
context.actorOf(Props[A], “A”)
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A
Foo
Guardian System Actor
Parental automatic supervision
context.actorOf(Props[A], “A”)
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A
B
Bar
Foo
C
B
E
A
D
C
Guardian System Actor
Parental automatic supervision
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A
B
Bar
Foo
C
B
E
A
D
C
Name resolution
Guardian System Actor
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A
B
Bar
Foo
C
B
E
A
D
C
/Foo
Name resolution
Guardian System Actor
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A
B
Bar
Foo
C
B
E
A
D
C
/Foo
/Foo/A
Name resolution
Guardian System Actor
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A
B
Bar
Foo
C
B
E
A
D
C
/Foo
/Foo/A
/Foo/A/B
Name resolution
Guardian System Actor
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A
B
Bar
Foo
C
B
E
A
D
C
/Foo
/Foo/A
/Foo/A/B
Name resolution
/Foo/A/D
Guardian System Actor
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ActorPath
val actorRef = system.actorFor("/user/pigdog")
val parent = context.actorFor("..")
val sibling = context.actorFor("../pigdog")
val refPath: ActorPath = actorRef.path
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ActorSelection
val selection =
system.actorSelection("/user/services/*")
selection ! "pigdog"
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Supervision
class MySupervisor extends Actor {
def supervisorStrategy = OneForOneStrategy({
case _: ActorKilledException => Stop
case _: ArithmeticException => Resume
case _: Exception => Restart
case _ => Escalate
},
maxNrOfRetries = None,
withinTimeRange = None)
def receive = {
case NewUser(name) =>
... = context.actorOf[User](name)
}
} Scala API
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Supervision
class MySupervisor extends Actor {
def supervisorStrategy = OneForOneStrategy({
case _: ActorKilledException => Stop
case _: ArithmeticException => Resume
case _: Exception => Restart
case _ => Escalate
},
maxNrOfRetries = None,
withinTimeRange = None)
def receive = {
case NewUser(name) =>
... = context.actorOf[User](name)
}
}
AllForOneStrategy
Scala API
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class FaultTolerantService extends Actor {
...
override def preRestart(
reason: Throwable, message: Option[Any]) = {
... // clean up before restart
}
override def postRestart(reason: Throwable) = {
... // init after restart
}
}
Manage failure
Scala API
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val buddy: ActorRef = ...
val watcher = context.actorOf(Props(
new Actor {
context.watch(buddy)
def receive = {
case Terminated(`buddy`) ⇒ …
}
}
))
watch/unwatch
Scala API
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Scale out
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New Remote Actors
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val actor = system.actorOf(Props[MyActor], “my-service”)
Name
Bind the actor to a name
Scala API
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Actor name is virtual and decoupled from how it is
deployed
Deployment
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Deployment
If no deployment configuration exists then actor is
deployed as local
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Deployment
The same system can be configured as distributed
without code change (even change at runtime)
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Deployment
Write as local but deploy as distributed in the cloud
without code change
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Deployment
Allows runtime to dynamically and adaptively change
topology
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akka {
actor {
deployment {
/my-service {
router = "round-robin"
nr-of-instances = 3
target {
nodes = ["wallace:2552", "gromit:2552"]
}
}
}
}
}
Deployment configuration
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Error
Kernel
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Node 1 Node 2
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‣ EventBus API
‣ Extensions
‣ ScalaSTM
‣ TypedActor 2.0
More news
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Akka 2.0+
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‣ Apache Camel
‣ AMQP
‣ Spring
Integration
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Get it and learn more
http://akka.io
http://typesafe.com
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EOF
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