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Back to the futures, actors and pipes: using Akka for large-scale data migration

Manuel Bernhardt, profile picture
Manuel Bernhardt

- The document discusses data migration from an old platform to a new Scala/Play implementation using Akka actors, futures, and pipes. - Futures are used to handle asynchronous operations, actors are used to organize complex asynchronous flows and deal with failures, and pipes are used to deal with asynchronous computation results inside actors. - Several lessons are discussed, including designing the system around the data structure, knowing the limits of the source system to avoid overloading it, and being aware of rate limits for cloud APIs.

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@ELMANU BACK < & future: ACTORS AND > PIPES < using akka for large-scale data migration manuel BERNHART
@ELMANU AGENDA • { BACKGROUND STORY • } FUTURES > PIPES < ACTORS • | LESSONS LEARNED
@ELMANU who is speaking? • freelance software consultant based in Vienna • Vienna Scala User Group • web, web, web • writing a book on reactive web-applications
@ELMANU [ { BACKGROUND STORY
@ELMANU talenthouse • www.talenthouse.com • based in Los Angeles • connecting brands and artists • 3+ million users
Back to the futures, actors and pipes: using Akka for large-scale data migration
Back to the futures, actors and pipes: using Akka for large-scale data migration
Back to the futures, actors and pipes: using Akka for large-scale data migration
Back to the futures, actors and pipes: using Akka for large-scale data migration
@ELMANU BACKGROUND STORY • old, slow (very slow) platform • re-implementation from scratch with Scala & Play • tight schedule, a lot of data to migrate
@ELMANU SOURCE SYSTEM
@ELMANU SOURCE SYSTEM DISCLAIMER: What follows is not intended as a bashing of the source system, but as a necessary explanation of its complexity in relation to data migration.
@ELMANU SOURCE SYSTEM
@ELMANU SOURCE SYSTEM
@ELMANU SOURCE SYSTEM
@ELMANU SOURCE SYSTEM
@ELMANU SOURCE SYSTEM
@ELMANU SOURCE SYSTEM
@ELMANU SOURCE SYSTEM
@ELMANU SOURCE SYSTEM
@ELMANU MIGRATION schedule •basically, one week-end •big-bang kind-of migration •if possible incremental migration beforehand
@ELMANU [ } FUTURES > PIPES < ACTORS
@ELMANU FUTURES
@ELMANU FUTURES •scala.concurrent.Future[T] •holds a value of type T •can either fail or succeed
@ELMANU FUTURES: HAPPY PATH import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global val futureSum: Future[Int] = Future { 1 + 1 } futureSum.map { sum => println("The sum is " + sum) }
@ELMANU FUTURES: SAD PATH import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ val futureDiv: Future[Int] = Future { 1 / 0 } val futurePrint: Future[Unit] = futureDiv.map { div => println("The division result is " + div) } Await.result(futurePrint, 1 second)
@ELMANU FUTURES: SAD PATH import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ val futureDiv: Future[Int] = Future { 1 / 0 } val futurePrint: Future[Unit] = futureDiv.map { div => println("The division result is " + div) } Await.result(futurePrint, 1 second) Avoid blocking if possible
@ELMANU FUTURES: SAD PATH import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ scala> Await.result(futureDiv, 1.second) java.lang.ArithmeticException: / by zero at $anonfun$1.apply$mcI$sp(<console>:11) at $anonfun$1.apply(<console>:11) at $anonfun$1.apply(<console>:11) at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24) at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24) at scala.concurrent.impl.ExecutionContextImpl $AdaptedForkJoinTask.exec(ExecutionContextImpl.scala:121) at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107) val futureDiv: Future[Int] = Future { 1 / 0 } futureDiv.map { div => println("The division result is " + div) } Await.result(futureDiv, 1 second)
@ELMANU FUTURES: SAD PATH import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ val futureDiv: Future[Int] = Future { 1 / 0 } val futurePrint: Future[Unit] = futureDiv.map { div => println("The division result is " + div) }.recover { case a: java.lang.ArithmeticException => println("What on earth are you trying to do?") } Await.result(futurePrint, 1 second) Be mindful of failure
@ELMANU FUTURES: SAD PATH •Exceptions are propagated up the chain •Without recover there is no guarantee that failure will ever get noticed!
@ELMANU COMPOSING FUTURES val futureA: Future[Int] = Future { 1 + 1 } val futureB: Future[Int] = Future { 2 + 2 } val futureC: Future[Int] = for { a <- futureA b <- futureB } yield { a + b }
@ELMANU COMPOSING FUTURES val futureC: Future[Int] = for { a <- Future { 1 + 1 } b <- Future { 2 + 2 } } yield { a + b }
@ELMANU COMPOSING FUTURES val futureC: Future[Int] = for { a <- Future { 1 + 1 } b <- Future { 2 + 2 } } yield { a + b } This runs in sequence Don’t do this
@ELMANU FUTURES: CALLBACKS import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global val futureDiv: Future[Int] = Future { 1 / 0 } futureDiv.onSuccess { case result => println("Result: " + result) } futureDiv.onFailure { case t: Throwable => println("Oh no!") }
@ELMANU using FUTURES •a Future { … } block that doesn’t do any I/O is code smell •use them in combination with the “right” ExecutionContext set-up •when you have blocking operations, wrap them into a blocking block
@ELMANU using FUTURES import scala.concurrent.blocking Future { blocking { DB.withConnection { implicit connection => val query = SQL("select * from bar") query() } } }
@ELMANU naming FUTURES
@ELMANU naming FUTURES “Say eventuallyMaybe one more time!”
@ELMANU ACTORS
@ELMANU ACTORS •lightweight objects •send and receive messages (mailbox) •can have children (supervision)
@ELMANU ACTORS Mailbox Mailbox akka://application/user/georgePeppard akka://application/user/audreyHepburn Mailbox akka://application/user/audreyHepburn/cat
@ELMANU ACTORS Mailbox Mailbox Holly, I'm in love with you. akka://application/user/georgePeppard akka://application/user/audreyHepburn akka://application/user/audreyHepburn/cat
@ELMANU ACTORS Mailbox Mailbox Holly, I'm in love with you. So what? akka://application/user/georgePeppard akka://application/user/audreyHepburn akka://application/user/audreyHepburn/cat
@ELMANU GETTING AN ACTOR import akka.actor._ class AudreyHepburn extends Actor { def receive = { ... } } val system: ActorSystem = ActorSystem() val audrey: ActorRef = system.actorOf(Props[AudreyHepburn])
@ELMANU SENDING AND RECEIVING MESSAGES case class Script(text: String) class AudreyHepburn extends Actor { def receive = { case Script(text) => read(text) } }
@ELMANU SENDING AND RECEIVING MESSAGES case class Script(text: String) class AudreyHepburn extends Actor { def receive = { case Script(text) => read(text) } } audrey ! Script(breakfastAtTiffany)
@ELMANU SENDING AND RECEIVING MESSAGES case class Script(text: String) class AudreyHepburn extends Actor { def receive = { case Script(text) => read(text) } } audrey ! Script(breakfastAtTiffany) “tell” - fire-forget
@ELMANU ASK PATTERN import akka.pattern.ask import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ implicit val timeout = akka.util.Timeout(1 second) val maybeAnswer: Future[String] = audrey ? "Where should we have breakfast?"
@ELMANU ASK PATTERN import akka.pattern.ask import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ implicit val timeout = akka.util.Timeout(1 second) val maybeAnswer: Future[String] = audrey ? "Where should we have breakfast?" “ask”
@ELMANU SUPERVISION class UserMigrator extends Actor { lazy val workers: ActorRef = context .actorOf[UserMigrationWorker] .withRouter(RoundRobinRouter(nrOfInstances = 100)) }
@ELMANU SUPERVISION class UserMigrator extends Actor { actor context lazy val workers: ActorRef = context .actorOf[UserMigrationWorker] .withRouter(RoundRobinRouter(nrOfInstances = 100)) } router type many children
@ELMANU SUPERVISION
@ELMANU SUPERVISION class UserMigrator extends Actor { lazy val workers: ActorRef = context .actorOf[UserMigrationWorker] .withRouter(RoundRobinRouter(nrOfInstances = 100)) override def supervisorStrategy: SupervisorStrategy = OneForOneStrategy(maxNrOfRetries = 3) { case t: Throwable => log.error(“A child died!”, t) Restart } }
@ELMANU PIPES
@ELMANU CECI EST UNE PIPE •Akka pattern to combine Futures and Actors •Sends the result of a Future to an Actor •Be careful with error handling
@ELMANU CECI EST UNE PIPE class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender() val download: Future[DownloadedFile] = WS.url(url).get().map { response => DownloadedFile( url, response.ahcResponse.getResponseBodyAsBytes ) } import akka.pattern.pipe download pipeTo originalSender } }
@ELMANU CECI EST UNE PIPE class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender() val download: Future[DownloadedFile] = WS.url(url).get().map { response => DownloadedFile( url, response.ahcResponse.getResponseBodyAsBytes ) } import akka.pattern.pipe download pipeTo originalSender } } This is how you pipe
@ELMANU CECI EST UNE PIPE class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender() val download: Future[DownloadedFile] = WS.url(url).get().map { response => DownloadedFile( url, response.ahcResponse.getResponseBodyAsBytes ) } import akka.pattern.pipe download pipeTo originalSender } } Keep reference to original sender - what follows is a Future!
@ELMANU CECI EST UNE PIPE class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender() val download: Future[DownloadedFile] = WS.url(url).get().map { response => DownloadedFile( url, response.ahcResponse.getResponseBodyAsBytes ) } import akka.pattern.pipe download pipeTo originalSender } } Wrap your result into something you can easily match against
@ELMANU CECI EST UNE PIPE class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender val download: Future[Array[Byte]] = WS.url(url).get().map { response => DownloadedFile( url, response.ahcResponse.getResponseBodyAsBytes ) } import akka.pattern.pipe download pipeTo originalSender } } Will this work?
@ELMANU PIPES AND error handling class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender() val download = WS.url(url).get().map { response => DownloadedFile(...) } recover { case t: Throwable => DownloadFileFailure(url, t) } Don’t forget to recover! import akka.pattern.pipe download pipeTo originalSender } }
@ELMANU SUMMARY •Futures: manipulate and combine asynchronous operation results •Actors: organise complex asynchronous flows, deal with failure via supervision •Pipes: deal with results of asynchronous computation inside of actors
@ELMANU [ | LESSONS LEARNED
@ELMANU design according to YOUR DATA User migrator Worker Worker Worker Worker Worker
@ELMANU design according to YOUR DATA Item migrator User item migrator Item migration worker Item migration worker User item migrator Item migration worker Item migration worker User item migrator Item migration worker Item migration worker design A
@ELMANU design according to YOUR DATA Item migrator User item migrator Item migration worker Item migration worker User item migrator Item migration worker Item migration worker User item migrator Item migration worker Item migration worker design A Not all users have the same amount of items
@ELMANU design according to YOUR DATA Item migrator Item migration worker User item migrator User item migrator User item migrator Item migration worker Item migration worker Item migration worker Item migration worker Item migration worker File fetcher File fetcher File uploader File uploader Soundcloud worker design B
@ELMANU design according to YOUR DATA Item migration worker User item migrator User item migrator Item migration worker Item migration worker Item migration worker Item migration worker Item migration worker File fetcher File fetcher File uploader File uploader Soundcloud worker Pools of actors design B Item migrator User item migrator
@ELMANU KNOW THE limits OF THY SOURCE SYSTEM
@ELMANU KNOW THE limits OF THY SOURCE SYSTEM
@ELMANU DATA MIGRATION SHOULD not BE A RACE •Your goal is to get the data, not to be as fast as possible •Be gentle to the legacy system(s)
@ELMANU CLOUD API STANDARDS •ISO-28601 Data formats in REST APIs •ISO-28700 Response times and failure communication of REST APIs •ISO-28701 Rate limits in REST APIs and HTTP error codes
@ELMANU CLOUD API STANDARDS •ISO-28601 Data formats in REST APIs •ISO-28700 Response times and failure communication of REST APIs •ISO-28701 Rate limits in REST APIs and HTTP error codes DREAM ON
@ELMANU NO STANDARDS! •The cloud is heterogenous •Response times, rate limits, error codes all different •Don’t even try to treat all systems the same
@ELMANU RATE limits
@ELMANU RATE limits •Read the docs - most cloud API docs will warn you about them •Design your actor system so that you can queue if necessary •Keep track of migration status
@ELMANU RATE limits •Example: Soundcloud API •500 Internal Server Error after seemingly random amount of requests
@ELMANU RATE limits •Example: Soundcloud API •500 Internal Server Error after seemingly random amount of requests Magic User-Agent WS .url("http://api.soundcloud.com/resolve.json") .withHeaders("User-Agent" -> “FOOBAR”) // the magic ingredient that // opens the door to Soundcloud
@ELMANU BLOCKING
@ELMANU seriously, do not BLOCK •Seems innocent at first to block from time to time •OutOfMemory after 8 hours of migration run is not very funny •You will end up rewriting your whole code to be async anyway
@ELMANU MISC •Unstable primary IDs in source system •Build a lot of small tools, be pragmatic •sbt-tasks (http://yobriefca.se/sbt-tasks/)
@ELMANU THE END
@ELMANU THE END QUESTIONS?

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Back to the futures, actors and pipes: using Akka for large-scale data migration

  • 1. @ELMANU BACK < & future: ACTORS AND > PIPES < using akka for large-scale data migration manuel BERNHART
  • 2. @ELMANU AGENDA • { BACKGROUND STORY • } FUTURES > PIPES < ACTORS • | LESSONS LEARNED
  • 3. @ELMANU who is speaking? • freelance software consultant based in Vienna • Vienna Scala User Group • web, web, web • writing a book on reactive web-applications
  • 4. @ELMANU [ { BACKGROUND STORY
  • 5. @ELMANU talenthouse • www.talenthouse.com • based in Los Angeles • connecting brands and artists • 3+ million users
  • 10. @ELMANU BACKGROUND STORY • old, slow (very slow) platform • re-implementation from scratch with Scala & Play • tight schedule, a lot of data to migrate
  • 12. @ELMANU SOURCE SYSTEM DISCLAIMER: What follows is not intended as a bashing of the source system, but as a necessary explanation of its complexity in relation to data migration.
  • 21. @ELMANU MIGRATION schedule •basically, one week-end •big-bang kind-of migration •if possible incremental migration beforehand
  • 22. @ELMANU [ } FUTURES > PIPES < ACTORS
  • 24. @ELMANU FUTURES •scala.concurrent.Future[T] •holds a value of type T •can either fail or succeed
  • 25. @ELMANU FUTURES: HAPPY PATH import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global val futureSum: Future[Int] = Future { 1 + 1 } futureSum.map { sum => println("The sum is " + sum) }
  • 26. @ELMANU FUTURES: SAD PATH import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ val futureDiv: Future[Int] = Future { 1 / 0 } val futurePrint: Future[Unit] = futureDiv.map { div => println("The division result is " + div) } Await.result(futurePrint, 1 second)
  • 27. @ELMANU FUTURES: SAD PATH import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ val futureDiv: Future[Int] = Future { 1 / 0 } val futurePrint: Future[Unit] = futureDiv.map { div => println("The division result is " + div) } Await.result(futurePrint, 1 second) Avoid blocking if possible
  • 28. @ELMANU FUTURES: SAD PATH import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ scala> Await.result(futureDiv, 1.second) java.lang.ArithmeticException: / by zero at $anonfun$1.apply$mcI$sp(<console>:11) at $anonfun$1.apply(<console>:11) at $anonfun$1.apply(<console>:11) at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24) at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24) at scala.concurrent.impl.ExecutionContextImpl $AdaptedForkJoinTask.exec(ExecutionContextImpl.scala:121) at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107) val futureDiv: Future[Int] = Future { 1 / 0 } futureDiv.map { div => println("The division result is " + div) } Await.result(futureDiv, 1 second)
  • 29. @ELMANU FUTURES: SAD PATH import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ val futureDiv: Future[Int] = Future { 1 / 0 } val futurePrint: Future[Unit] = futureDiv.map { div => println("The division result is " + div) }.recover { case a: java.lang.ArithmeticException => println("What on earth are you trying to do?") } Await.result(futurePrint, 1 second) Be mindful of failure
  • 30. @ELMANU FUTURES: SAD PATH •Exceptions are propagated up the chain •Without recover there is no guarantee that failure will ever get noticed!
  • 31. @ELMANU COMPOSING FUTURES val futureA: Future[Int] = Future { 1 + 1 } val futureB: Future[Int] = Future { 2 + 2 } val futureC: Future[Int] = for { a <- futureA b <- futureB } yield { a + b }
  • 32. @ELMANU COMPOSING FUTURES val futureC: Future[Int] = for { a <- Future { 1 + 1 } b <- Future { 2 + 2 } } yield { a + b }
  • 33. @ELMANU COMPOSING FUTURES val futureC: Future[Int] = for { a <- Future { 1 + 1 } b <- Future { 2 + 2 } } yield { a + b } This runs in sequence Don’t do this
  • 34. @ELMANU FUTURES: CALLBACKS import scala.concurrent._ import scala.concurrent.ExecutionContext.Implicits.global val futureDiv: Future[Int] = Future { 1 / 0 } futureDiv.onSuccess { case result => println("Result: " + result) } futureDiv.onFailure { case t: Throwable => println("Oh no!") }
  • 35. @ELMANU using FUTURES •a Future { … } block that doesn’t do any I/O is code smell •use them in combination with the “right” ExecutionContext set-up •when you have blocking operations, wrap them into a blocking block
  • 36. @ELMANU using FUTURES import scala.concurrent.blocking Future { blocking { DB.withConnection { implicit connection => val query = SQL("select * from bar") query() } } }
  • 38. @ELMANU naming FUTURES “Say eventuallyMaybe one more time!”
  • 40. @ELMANU ACTORS •lightweight objects •send and receive messages (mailbox) •can have children (supervision)
  • 41. @ELMANU ACTORS Mailbox Mailbox akka://application/user/georgePeppard akka://application/user/audreyHepburn Mailbox akka://application/user/audreyHepburn/cat
  • 42. @ELMANU ACTORS Mailbox Mailbox Holly, I'm in love with you. akka://application/user/georgePeppard akka://application/user/audreyHepburn akka://application/user/audreyHepburn/cat
  • 43. @ELMANU ACTORS Mailbox Mailbox Holly, I'm in love with you. So what? akka://application/user/georgePeppard akka://application/user/audreyHepburn akka://application/user/audreyHepburn/cat
  • 44. @ELMANU GETTING AN ACTOR import akka.actor._ class AudreyHepburn extends Actor { def receive = { ... } } val system: ActorSystem = ActorSystem() val audrey: ActorRef = system.actorOf(Props[AudreyHepburn])
  • 45. @ELMANU SENDING AND RECEIVING MESSAGES case class Script(text: String) class AudreyHepburn extends Actor { def receive = { case Script(text) => read(text) } }
  • 46. @ELMANU SENDING AND RECEIVING MESSAGES case class Script(text: String) class AudreyHepburn extends Actor { def receive = { case Script(text) => read(text) } } audrey ! Script(breakfastAtTiffany)
  • 47. @ELMANU SENDING AND RECEIVING MESSAGES case class Script(text: String) class AudreyHepburn extends Actor { def receive = { case Script(text) => read(text) } } audrey ! Script(breakfastAtTiffany) “tell” - fire-forget
  • 48. @ELMANU ASK PATTERN import akka.pattern.ask import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ implicit val timeout = akka.util.Timeout(1 second) val maybeAnswer: Future[String] = audrey ? "Where should we have breakfast?"
  • 49. @ELMANU ASK PATTERN import akka.pattern.ask import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.duration._ implicit val timeout = akka.util.Timeout(1 second) val maybeAnswer: Future[String] = audrey ? "Where should we have breakfast?" “ask”
  • 50. @ELMANU SUPERVISION class UserMigrator extends Actor { lazy val workers: ActorRef = context .actorOf[UserMigrationWorker] .withRouter(RoundRobinRouter(nrOfInstances = 100)) }
  • 51. @ELMANU SUPERVISION class UserMigrator extends Actor { actor context lazy val workers: ActorRef = context .actorOf[UserMigrationWorker] .withRouter(RoundRobinRouter(nrOfInstances = 100)) } router type many children
  • 53. @ELMANU SUPERVISION class UserMigrator extends Actor { lazy val workers: ActorRef = context .actorOf[UserMigrationWorker] .withRouter(RoundRobinRouter(nrOfInstances = 100)) override def supervisorStrategy: SupervisorStrategy = OneForOneStrategy(maxNrOfRetries = 3) { case t: Throwable => log.error(“A child died!”, t) Restart } }
  • 55. @ELMANU CECI EST UNE PIPE •Akka pattern to combine Futures and Actors •Sends the result of a Future to an Actor •Be careful with error handling
  • 56. @ELMANU CECI EST UNE PIPE class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender() val download: Future[DownloadedFile] = WS.url(url).get().map { response => DownloadedFile( url, response.ahcResponse.getResponseBodyAsBytes ) } import akka.pattern.pipe download pipeTo originalSender } }
  • 57. @ELMANU CECI EST UNE PIPE class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender() val download: Future[DownloadedFile] = WS.url(url).get().map { response => DownloadedFile( url, response.ahcResponse.getResponseBodyAsBytes ) } import akka.pattern.pipe download pipeTo originalSender } } This is how you pipe
  • 58. @ELMANU CECI EST UNE PIPE class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender() val download: Future[DownloadedFile] = WS.url(url).get().map { response => DownloadedFile( url, response.ahcResponse.getResponseBodyAsBytes ) } import akka.pattern.pipe download pipeTo originalSender } } Keep reference to original sender - what follows is a Future!
  • 59. @ELMANU CECI EST UNE PIPE class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender() val download: Future[DownloadedFile] = WS.url(url).get().map { response => DownloadedFile( url, response.ahcResponse.getResponseBodyAsBytes ) } import akka.pattern.pipe download pipeTo originalSender } } Wrap your result into something you can easily match against
  • 60. @ELMANU CECI EST UNE PIPE class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender val download: Future[Array[Byte]] = WS.url(url).get().map { response => DownloadedFile( url, response.ahcResponse.getResponseBodyAsBytes ) } import akka.pattern.pipe download pipeTo originalSender } } Will this work?
  • 61. @ELMANU PIPES AND error handling class FileFetcher extends Actor { def receive = { case FetchFile(url) => val originalSender = sender() val download = WS.url(url).get().map { response => DownloadedFile(...) } recover { case t: Throwable => DownloadFileFailure(url, t) } Don’t forget to recover! import akka.pattern.pipe download pipeTo originalSender } }
  • 62. @ELMANU SUMMARY •Futures: manipulate and combine asynchronous operation results •Actors: organise complex asynchronous flows, deal with failure via supervision •Pipes: deal with results of asynchronous computation inside of actors
  • 63. @ELMANU [ | LESSONS LEARNED
  • 64. @ELMANU design according to YOUR DATA User migrator Worker Worker Worker Worker Worker
  • 65. @ELMANU design according to YOUR DATA Item migrator User item migrator Item migration worker Item migration worker User item migrator Item migration worker Item migration worker User item migrator Item migration worker Item migration worker design A
  • 66. @ELMANU design according to YOUR DATA Item migrator User item migrator Item migration worker Item migration worker User item migrator Item migration worker Item migration worker User item migrator Item migration worker Item migration worker design A Not all users have the same amount of items
  • 67. @ELMANU design according to YOUR DATA Item migrator Item migration worker User item migrator User item migrator User item migrator Item migration worker Item migration worker Item migration worker Item migration worker Item migration worker File fetcher File fetcher File uploader File uploader Soundcloud worker design B
  • 68. @ELMANU design according to YOUR DATA Item migration worker User item migrator User item migrator Item migration worker Item migration worker Item migration worker Item migration worker Item migration worker File fetcher File fetcher File uploader File uploader Soundcloud worker Pools of actors design B Item migrator User item migrator
  • 69. @ELMANU KNOW THE limits OF THY SOURCE SYSTEM
  • 70. @ELMANU KNOW THE limits OF THY SOURCE SYSTEM
  • 71. @ELMANU DATA MIGRATION SHOULD not BE A RACE •Your goal is to get the data, not to be as fast as possible •Be gentle to the legacy system(s)
  • 72. @ELMANU CLOUD API STANDARDS •ISO-28601 Data formats in REST APIs •ISO-28700 Response times and failure communication of REST APIs •ISO-28701 Rate limits in REST APIs and HTTP error codes
  • 73. @ELMANU CLOUD API STANDARDS •ISO-28601 Data formats in REST APIs •ISO-28700 Response times and failure communication of REST APIs •ISO-28701 Rate limits in REST APIs and HTTP error codes DREAM ON
  • 74. @ELMANU NO STANDARDS! •The cloud is heterogenous •Response times, rate limits, error codes all different •Don’t even try to treat all systems the same
  • 76. @ELMANU RATE limits •Read the docs - most cloud API docs will warn you about them •Design your actor system so that you can queue if necessary •Keep track of migration status
  • 77. @ELMANU RATE limits •Example: Soundcloud API •500 Internal Server Error after seemingly random amount of requests
  • 78. @ELMANU RATE limits •Example: Soundcloud API •500 Internal Server Error after seemingly random amount of requests Magic User-Agent WS .url("http://api.soundcloud.com/resolve.json") .withHeaders("User-Agent" -> “FOOBAR”) // the magic ingredient that // opens the door to Soundcloud
  • 80. @ELMANU seriously, do not BLOCK •Seems innocent at first to block from time to time •OutOfMemory after 8 hours of migration run is not very funny •You will end up rewriting your whole code to be async anyway
  • 81. @ELMANU MISC •Unstable primary IDs in source system •Build a lot of small tools, be pragmatic •sbt-tasks (http://yobriefca.se/sbt-tasks/)
  • 83. @ELMANU THE END QUESTIONS?