![Enable clustering
akka {
actor {
provider = "akka.cluster.ClusterActorRefProvider"
...
}
extensions = ["akka.cluster.Cluster"]
cluster {
seed-nodes = [
"akka://ClusterSystem@127.0.0.1:2551",
"akka://ClusterSystem@127.0.0.1:2552"
]
}
}](https://image.slidesharecdn.com/akka-cluster-jdays-2012-121205042542-phpapp01/85/Akka-Distributed-by-Design-35-320.jpg)
Akka: Distributed by Design
- 1. Distributed by Design Patrik Nordwall @patriknw
- 2. outline actors remote actors rise of the cluster when the cluster grows up
- 3. What is an Actor? • Akka's unit of computation is called an Actor • Actors are purely reactive components: – a mailbox – behavior & state – scheduled to run when sent a message • Each actor has a parent, handling its failures
- 4. Event-driven Thread Actor Behavior State
- 5. Define Actor Define the message(s) the Actor should be able to respond to public class Greeting implements Serializable { public final String who; public Greeting(String who)the Actor class = who; } Define { this.who } public class GreetingActor extends UntypedActor { LoggingAdapter log = Logging.getLogger(getContext().system(), this); int counter = 0; public void onReceive(Object message) { if (message instanceof Greeting) { counter++; log.info("Hello #" + counter + " " + ((Greeting) message).who); } } Define the Actor’s behavior }
- 6. Create Actor public class Greeting implements Serializable { public final String who; public Greeting(String who) { this.who = who; } } public class GreetingActor extends UntypedActor { LoggingAdapter log = Logging.getLogger(getContext().system(), this); int counter = 0; public void onReceive(Object message) { if (message instanceof Greeting) { counter++; log.info("Hello #" + counter + " " + ((Greeting) message).who); Actor configuration } Create an Actor system } } ActorSystem system = ActorSystem.create("MySystem"); ActorRef greeter = system.actorOf(new Props(GreetingActor.class), "greeter"); You get an ActorRef back Create the Actor Give it a name
- 7. Actors can form hierarchies Guardian System Actor system.actorOf( Foo Bar new Props(Foo.class), “Foo”); getContext().actorOf( A A C new Props(A.class), “A”); B E C B D
- 8. Name resolution - like a file-system Guardian System Actor /Foo Foo Bar /Foo/A A C A /Foo/A/B B E C B D /Foo/A/D
- 9. Send Message public class Greeting implements Serializable { public final String who; public Greeting(String who) { this.who = who; } } public class GreetingActor extends UntypedActor { LoggingAdapter log = Logging.getLogger(getContext().system(), this); int counter = 0; public void onReceive(Object message) { if (message instanceof Greeting) { counter++; log.info("Hello #" + counter + " " + ((Greeting) message).who); } } } ActorSystem system = ActorSystem.create("MySystem"); ActorRef greeter = system.actorOf(new Props(GreetingActor.class), "greeter"); greeter.tell(new Greeting("Charlie Parker"), null); Send the message
- 10. Full example public class Greeting implements Serializable { public final String who; public Greeting(String who) { this.who = who; } } public class GreetingActor extends UntypedActor { LoggingAdapter log = Logging.getLogger(getContext().system(), this); int counter = 0; public void onReceive(Object message) { if (message instanceof Greeting) { counter++; log.info("Hello #" + counter + " " + ((Greeting) message).who); } else { unhandled(message); } } } ActorSystem system = ActorSystem.create("MySystem"); ActorRef greeter = system.actorOf(new Props(GreetingActor.class), "greeter"); greeter.tell(new Greeting("Charlie Parker"), null);
- 11. Distributa ble by Design
- 13. Node 1 Node 2 Error Kernel
- 14. Create Actor ActorRef greeter = system.actorOf(new Props( GreetingActor.class), "greeter");
- 15. Remote Deployment Just feed the ActorSystem with this configuration Configure a Remote Provider akka { For the Greeter actor { actor provider = akka.remote.RemoteActorRefProvider deployment { /greeter { remote = akka://MySystem@machine1:2552 } } Define Remote Path } Protocol Actor System Hostname Port } Zero code changes
- 16. Remote Lookup ActorRef greeter = system.actorFor( "akka://MySystem@machine1:2552/user/greeter" );
- 17. Can you see the problem?
- 18. Fixed Addresses akka { actor { provider = akka.remote.RemoteActorRefProvider deployment { /greeter { remote = akka://MySystem@machine1:2552 } } } } ActorRef greeter = system.actorFor( "akka://MySystem@machine1:2552/user/greeter" );
- 19. Akka Cluster
- 20. Akka Cluster 2.1 rimental p review in 2.1 Cluster is expe • Gossip-based Cluster Membership • Failure Detector • Cluster DeathWatch • Cluster-Aware Routers
- 21. Cluster Membership • Node ring à la Riak / Dynamo • Gossip-protocol for state dissemination • Vector Clocks to detect convergence
- 22. Node ring with gossiping members Member Node Member Member Node Node Member Member Node Node Gossip Member Member Node Node Member Member Node Node Member Node
- 23. Vector Clock • Vector Clocks are used to: - Generate a partial ordering of events in a distributed system - Detecting causality violations • We use Vector Clocks to to reconcile and merge differences in cluster state
- 24. Gossiping Protocol Used for: – Cluster Membership – Configuration data – Leader Determination – Partitioning data – Naming Service
- 25. Push/Pull Gossip • Push – sender only sends versions (Vector Clock) • Pull – receiver only asks for information for which it has an outdated version • Partly biased – send fraction of gossip to nodes with older state
- 26. Cluster Convergence • When each Node has seen the same Vector Clock • unreachable nodes will fail this • mark nodes DOWN to proceed – manual Ops intervention – automatic action
- 27. Member States • JOINING • UP • LEAVING • EXITING • DOWN • REMOVED
- 28. Leader • Any node can be the leader • Just takes the role of being a leader • Is deterministically recognized by all nodes – always the first member in the sorted membership ring
- 29. Cluster Events public class Listener extends UntypedActor { public void onReceive(Object message) { if (message instanceof MemberUp) { // ... } } } ActorRef listener = system.actorOf(new Props(Listener.class), "listener"); Cluster.get(system).subscribe(listener, MemberEvent.class);
- 30. Cluster Events public class Listener extends UntypedActor { public void onReceive(Object message) { if (message instanceof MemberUp) { MemberUp mUp = (MemberUp) message; getContext().actorFor(mUp.address() + "/user/greeter").tell( new Greeting("Charlie Parker"), getSelf()); } } } ActorRef listener = system.actorOf(new Props(Listener.class), "listener"); Cluster.get(system).subscribe(listener, MemberEvent.class);
- 31. Phi Accrual Failure Detector regular messages A B • B monitors A • Sample inter-arrival time to expect next beat • B measures continuum of deadness of A http://ddg.jaist.ac.jp/pub/HDY+04.pdf
- 32. Selective Failure Detection Member Node Member Member Node Node Member Member Node Node Heartbeat Member Member Node Node Member Member Node Member Node Node
- 33. Selective Failure Detection Member Node Member Member Node Node Member Member Node Node Heartbeat Member Member Node Node Member Member Node Member Node Node
- 34. Cluster DeathWatch • Triggered by marking node «A» DOWN – Tell parents of their lost children on «A» – Kill all children of actors on «A» – Send Terminated for actors on «A»
- 35. Enable clustering akka { actor { provider = "akka.cluster.ClusterActorRefProvider" ... } extensions = ["akka.cluster.Cluster"] cluster { seed-nodes = [ "akka://ClusterSystem@127.0.0.1:2551", "akka://ClusterSystem@127.0.0.1:2552" ] } }
- 36. Load Balancing
- 37. Routers ActorRef routerActor = getContext().actorOf( new Props(ExampleActor.class). withRouter(new RoundRobinRouter(nrOfInstances)) );
- 38. …or from config akka.actor.deployment { /path/to/actor { router = round-robin nr-of-instances = 5 } }
- 39. Configure a clustered router akka.actor.deployment { /statsService/workerRouter { router = consistent-hashing nr-of-instances = 100 cluster { enabled = on max-nr-of-instances-per-node = 3 allow-local-routees = on } } }
- 40. Multi Node Testing object MultiNodeSampleConfig extends MultiNodeConfig { val node1 = role("node1") val node2 = role("node2") } "A MultiNodeSample" must { "wait for all nodes to enter a barrier" in { enterBarrier("startup") } }
- 41. Multi Node Testing "send to and receive from a remote node" in { runOn(node1) { enterBarrier("deployed") val ponger = system.actorFor(node(node2) / "user" / "ponger") ponger ! "ping" expectMsg("pong") } runOn(node2) { system.actorOf(Props(new Actor { def receive = { case "ping" => sender ! "pong" } }), "ponger") enterBarrier("deployed") }
- 42. … when the Cluster grows up
- 43. Adaptive Load Balancing • Metrics collected and spread – Heap memory – CPU, system load • Adaptive Router – Biased random with weights based on capacity
- 44. One tree to rule them all • One Actor tree per node • Cluster tree is mapped to local sub-trees
- 45. One tree to rule them all
- 46. The Magic Sauce • User code only sees cluster://... names • ActorRef becomes repointable – local – remote • Can now move actors around transparently – Actor encapsulation makes it possible
- 47. What does this enable? • Actor migration • Actor replication • Automatic cluster partitioning – later also based on runtime metrics • Node fail-over – first for stateless actors – later for stateful actors using event sourcing ➾ Fault Tolerance & Distribution
- 48. Cluster Specification doc.akka.io/docs/akka/snapshot/cluster/cluster.html Cluster User Guide doc.akka.io/docs/akka/snapshot/cluster/cluster-usage-scala.html doc.akka.io/docs/akka/snapshot/cluster/cluster-usage-java.html Cluster Code github.com/akka/akka/tree/master/akka-cluster
- 49. get it and learn more http://akka.io http://letitcrash.com http://typesafe.com
- 50. E0F