System Integration with Akka and Apache Camel

Connecting Akka to the Rest of the World System integration with Akka and Apache Camel by Martin Krasser

About me • Freelance software engineer, architect – eHealth application integration (Java, Scala, Groovy) – Bioinformatics, Cheminformatics (C++, Java) – … • Open source committer – Akka – Camel – Scalaz-Camel – … • Java since 1998 • Scala since 2009 • Twitter: @mrt1nz

Overview • Introduction – Camel – Akka • Akka-Camel integration – Consumer actors – Producer actors – Actor components • Comparison – Camel routes – Akka-Camel routes – Scalaz-Camel routes

Apache Camel • Integration framework written in Java – Open source, Apache 2 license – http://camel.apache.org • Enterprise Integration Patterns (EIP) – G. Hohpe, B. Woolf • Domain-specific language (DSL) – Internal: Java, Scala – External: XML/Spring • Pluggable protocol and API bindings – HTTP, FTP, JMS, File … and approx. 100 more – Camel “components” http://camel.apache.org/components.html

Apache Camel • Usage in Scala applications – Camel Java/Scala DSL • http://camel.apache.org – Akka-Camel integration module • http://akka.io/docs/akka-modules/1.1.2/modules/camel.html – Scalaz-Camel DSL • https://github.com/krasserm/scalaz-camel

Apache Camel • Routing example D D HTTP jms:queue:docs JMS HTTP Filter Endpoint Endpoint http://example.org/docs Java DSL: from("jms:queue:docs") .filter().xpath("/person[@name='Jon']") .to("http:example.org/docs"); Scala DSL: "jms:queue:docs" when(_.in == "…") to("http:example.org/docs");

Apache Camel • Messaging endpoints – Configured via endpoint URI • "jms:queue:docs" • "http://example.org/docs" • … – Endpoint consumer: from(uri) – Endpoint producer: to(uri) • Message processors … – Configured via fluent API • filter().xpath("…") • transform(body().append("…")) • … – Custom Java/Scala code (Processor interface)

Akka • Platform for event-driven, scalable and fault- tolerant architectures on the JVM • Concurrency – Actors, agents, dataflow, STM • Scalability Core – Remote actors, cluster membership Services • Fault tolerance – Local and remote actor supervision

Akka • Add-on modules – akka-camel • Camel integration (untyped actors) – akka-camel-typed • Camel integration (typed actors) – akka-kernel • Microkernel – akka-scalaz • Scalaz support – akka-spring • Spring integration – …

Akka • Actor model – Mathematical model of concurrent computation – Carl Hewitt, 1973 • Akka actor – Encapsulates state – Encapsulates behavior – Exchanges messages – Mailbox – Event-driven – Single-threaded • API – Scala – Java

Akka • Actor model benefits – Easier to reason about – Raised abstraction level – Easier to avoid • Race conditions • Dead locks • Starvation • Live locks

Akka Actors • Receive messages import akka.actor.Actor // actor definition class ExampleActor extends Actor { def receive = { case "test" => … case _ => … } } // create actor reference (ActorRef) val actor = Actor.actorOf[ExampleActor] // start actor actor.start

Akka Actors • Send messages – Fire-Forget actor ! "test"

Akka Actors • Send messages – Send-And-Receive-Eventually actor !! "test" match { case Some(result) => … // process result case None => … // timeout } uses Future under the hood (with timeout)

Akka Actors • Send messages – Send-And-Receive-Future val future = actor !!! "test" future.await val result = future.get returns Future directly

Akka-Camel Integration • Exchange messages with Akka actors via – HTTP, FTP, JMS, File … and approx. 100 more – Any Camel component can be used (pluggable) • Integration layer of Akka – Consumer actors: receive message from Camel endpoints – Producer actors: produce messages to Camel endpoints – Message exchange patterns (MEPs): in-out and in-only • Leverages Camel’s asynchronous routing engine – Asynchronous completion of message exchange – No threads blocked waiting for response messages, for example

Consumer Actors • Basic example – TCP consumer • import akka.actor._ import akka.camel._ class TcpConsumer extends Actor with Consumer { def endpointUri = "mina:tcp://localhost:6200?textline=true" def receive = { case Message(body, headers) => { self.reply("received %s" format body) } } } – Camel component: camel-mina – MEP: in-out

Consumer Actors • Basic example – TCP consumer activation import akka.actor._ import akka.camel._ // Consumer actors require a running CamelService CamelServiceManager.startCamelService // Activate TCP endpoint (asynchronously) Actor.actorOf[TcpConsumer].start – Asynchronous activation of consumer endpoint

Consumer Actors • Basic example – TCP consumer activation import akka.actor._ import akka.camel._ // Consumer actors require a running CamelService val service = CamelServiceManager.startCamelService // Wait for TCP endpoint activation service.awaitEndpointActivation(1) { Actor.actorOf[TcpConsumer].start } – Wait for endpoint activation – Useful for testing purposes

Consumer Actors • Basic example – TCP consumer deactivation import akka.actor._ import akka.camel._ val service: CamelService = … val tcpConsumer: ActorRef = … // deactivate TCP endpoint (asynchronously) tcpConsumer.stop // … or wait for TCP endpoint deactivation service.awaitEndpointDeactivation(1) { tcpConsumer.stop }

Consumer Actors • Basic example – HTTP consumer class HttpConsumer extends Actor with Consumer { def endpointUri = "jetty:http://localhost:8080/example" def receive = { case msg: Message => { self.reply("received %s" format msg.bodyAs[String]) } } } – Camel component: camel-jetty – MEP: in-out – Jetty continuations used internally – Camel type converter (msg.bodyAs[…])

Consumer Actors • Basic example – JMS consumer class JMSConsumer extends Actor with Consumer { def endpointUri = "jms:queue:example" def receive = { case Message(body, headers) => ... } } – Camel component: camel-jms – MEP: in-only

Consumer Actors • Basic example – IMAP consumer class MailConsumer extends Actor with Consumer { def endpointUri = "imap://admin@mymailserver.com?password=secret" def receive = { case Message(body, headers) => ... } } – Camel component: camel-mail – MEP: in-only

Consumer Actors • Basic example – Scheduled consumer class ScheduledConsumer extends Actor with Consumer { def endpointUri = "quartz://example?cron=0/2+*+*+*+*+?" def receive = { case tick => ... } } – Camel component: camel-quartz – MEP: in-only

Consumer Actors • Acknowledgements import akka.camel.Ack ... class FileConsumer extends Actor with Consumer { override def autoack = false // default is true def endpointUri = "file:messages/in?delete=true" def receive = { case Message(body, headers) => { // ... self.reply(Ack) // delete consumed file } } } – Camel component: camel-file – MEP: in-only – Application-level acknowledgement (Ack)

Consumer Actors • Failure replies import akka.camel.Failure ... class FileConsumer extends Actor with Consumer { override def autoack = false // default is true def endpointUri = "file:messages/in?delete=true" def receive = { case Message(body, headers) => { // ... self.reply(Failure(reason)) // redeliver file } } } – Application-level negative acknowledgement (Failure) – Redelivery works also with JMS endpoints, for example – Failure replies can also be used with in-out MEP

Consumer Actors • Failure replies – Should not be made within receive – Let consumer actors crash (on Exception) – Use a supervisor for failure replies

Consumer Actors • Supervised consumer class SupervisedFileConsumer extends Actor with Consumer { override def autoack = false def endpointUri = "file:messages/in?delete=true" def receive = { case Message(body, headers) => { // if exception thrown: actor is restarted or stopped // else self.reply(Ack) // delete file } } override def preRestart(reason: scala.Throwable) { self.reply_?(Failure(reason)) // redeliver file } override def postStop() { self.reply_?(Failure(…)) // or Ack to delete file } }

Consumer Actors • Supervised consumer import akka.actor._ import akka.config.Supervision._ // Create consumer actor reference val consumer = Actor.actorOf[new SupervisedFileConsumer] // Create supervisor for consumer actor val supervisor = Supervisor( SupervisorConfig( OneForOneStrategy( List(classOf[Exception]), 5, 10000), Supervise(consumer, Permanent) :: Nil)) – Restart on any Exception – 5 restart attempts within 10 seconds

Consumer Actors • Simplified failure reporting – override def blocking = true – Pros • No need for setting up a supervisor • No need to catch exception within receive • No need to self.reply(Failure(…)) – Cons • Endpoint communicates with actor via !! • Thread blocked waiting for Ack

Consumer Actors • Simplified failure reporting class FileConsumer extends Actor with Consumer { override def blocking = true override def autoack = false def endpointUri = "file:messages/in?delete=true" def receive = { case Message(body, headers) => { // if exception thrown: endpoint receives it // else self.reply(Ack) // delete file } } }

Typed Consumer Actors • Basic example – HTTP/JMS consumer import akka.actor._ import akka.camel._ import org.apache.camel.{Body, Header} trait TypedConsumer { @consume("jetty:http://localhost:8080/example") // in-out def foo(s: String): String @consume("jms:queue:example") // in-only def bar (@Body s: String, @Header("priority") p: Integer) : Unit } class TypedConsumerImpl extends TypedActor with TypedConsumer { def foo(s: String) = "received %s" format s def bar(s: String, p: Integer) = println("received %s (priority = %d)" format(s, p)) }

Typed Consumer Actors • Annotations – Consumer endpoints • @consume(endpointURI) – Parameter bindings • @Body • @Header •…

Typed Consumer Actors • Basic example – HTTP/JMS consumer activation import akka.actor._ import akka.camel._ val service = CamelServiceManager.startCamelService // Activate HTTP and JMS endpoints (asynchronously) TypedActor.newInstance( classOf[TypedConsumer], classOf[TypedConsumerImpl]) // … or wait for HTTP and JMS endpoint activation service.awaitEndpointActivation(2) { TypedActor.newInstance( classOf[TypedConsumer], classOf[TypedConsumerImpl]) }

Producer Actors • Basic example – HTTP producer import akka.actor._ import akka.camel._ class HttpProducer extends Actor with Producer { def endpointUri = "jetty:http://localhost:8080/example" } – Camel component: camel-jetty – MEP: in-out – receive inherited from Producer trait – Jetty’s async HTTP client used internally

Producer Actors • Basic example – HTTP producer activation import akka.actor._ import akka.camel._ // Producer actors require an initialized CamelContext CamelServiceManager.startCamelService // activate producer actor val producer = Actor.actorOf[HttpProducer].start // POST test message to http://localhost:8080/example producer !! "test" match { case Some(m: Message) => … case Some(f: Failure) => … case None => … } // ! and !!! can also be used

Producer Actors • Basic example – JMS producer class JmsProducer extends Actor with Producer { def endpointUri = "jms:queue:example" override def oneway = true } – Camel component: camel-jms – MEP: in-only

Producer Actors • oneway = false (default) – Initiates an in-out ME with endpoint – Replies result to initial sender • oneway = true – Initiates an in-only ME with endpoint – No reply to sender • receiveAfterProduce – Change default reply behaviour

Producer Actors • Custom replies class JmsProducer extends Actor with Producer { def endpointUri = "jms:queue:example" override def oneway = true override def receiveAfterProduce = { case m: Message => self.reply("enqueue succeeded") case f: Failure => self.reply("enqueue failed") } }

Producer Actors • Forward results class HttpProducer extends Actor with Producer { val target: ActorRef = … def endpointUri = "jetty:http://localhost:8080/example" override def receiveAfterProduce = { case msg => target forward msg } } – Chaining of producer actors (pipelines) – Related: Future composition

Producer Actors • Future composition val producer1 = Actor.actorOf[HttpProducer1].start val producer2 = Actor.actorOf[HttpProducer2].start // monadic future composition (non-blocking) val future = for { m1: Message <- producer1 !!! Message("test") m2: Message <- producer2 !!! m1 } yield m2 // blocks until result is available – Producer Message val result: pipeline = future.get

Actor Components • Are Camel components – Can be used in any Camel route • actor Camel component – Send messages to untyped actors – Provided by akka-camel module • typed-actor Camel component – Send messages to typed actors – Provided by akka-camel-typed module – Extension of Camel’s bean component • Used by akka-camel internally – Routes to consumer actors

Actor Components • actor endpoint URI – actor:uuid:[<actor-uuid>][?<params>] • Parameters – autoack: Boolean • System or application-level acknowledgements – blocking: Boolean • Use ! or !! for sending messages to actor • Supported message headers – CamelActorIdentifier • Dynamic routing to actors

Actor Components • Example import akka.actor._ // can be any actor (no need for Consumer) val actor = Actor.actorOf[SomeActor].start // ... // Camel route from JMS endpoint to actor from("jms:queue:example") .to("actor:uuid:%s?autoack=false" format actor.uuid) – actor receives messages of type Message

Comparison • Criteria – Connectivity – Message processing – Route composition – Other • High-level • Incomplete

Camel Routes • Connectivity – Camel components/endpoints • Message processing – Processor interface • Predefined processors (all known EIPs) • Custom processors – Concurrent execution of Processor instances – Mutable messages

Camel Routes • Route composition – Camel DSL (Java, Scala, XML) • Other – No built-in mechanism for distributing routes (except via endpoints) – Distribution addressed by ServiceMix and FuseSource Fabric, for example

Akka-Camel Routes • Connectivity – Camel components/endpoints managed by • Consumer actors • Producer actors • Message processing – Actor • Predefined (a few in akka.actor.routing) • Custom – Sequential execution of actor instance – Immutable messages

Akka-Camel Routes • Route composition – Wiring actors (low-level) – Future composition – … – No integration DSL (yet) • Other – Easy to implementing stateful EIPs (aggregator, resequencer …) – Strong built-in mechanisms for distribution, scalability and fault-tolerance – Basis for a distributed and scalable Enterprise Service Bus (?)

Scalaz-Camel Routes • Connectivity – Camel components/endpoints • Message processing – Scala functions • Predefined (some EIPs) • Custom – Concurrent execution – Immutable messages

Scalaz-Camel Routes • Route composition – Based on functional programming concepts • Message processors chained via Kleisli composition (>=>) – Continuation-based approach • scala.Responder used as continuation monad – Direct-style DSL • Other – Configurable concurrency strategies – Camel processors can be re-used – Akka integration

Scalaz-Camel Routes • Example // custom message processor val validate: MessageProcessor = ... // Kleisli composition of route (+ implicit conversions) val vroute = validate >=> oneway >=> to("jms:queue:valid") >=> { m: Message => m.setBody("order accepted") } // consume messages via HTTP and error handling routes from(jetty:http://localhost:8080/orders) attempt { vroute } fallback { case e: ValidationException => { m: Message => ... } >=> failWith(e) case _ => ... } – Details at https://github.com/krasserm/scalaz-camel

System Integration with Akka and Apache Camel

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