Scaling the Klout API with Scala, Akka, and Play

futureBad.scala

def blockingAndVerbose: Profile = {
    val futureName = name()
    val futureScore = score()
    val futureFriends = Friends()

    val nameResult = Await.result(futureName, 10 seconds)
    val scoreResult = Await.result(futureScore, 10 seconds)
    val friendsResult = Await.result(futureFriends, 10 seconds)

    Profile(nameResult, scoreResult, friendsResult)
}

futureGood.scala

def nonBlockingComposition: Future[Profile] = {
    // NOTE: We declare these up here so they start in parallel. This is required
    // because of how for expressions get expanded to maps and flatMaps.
    val futureName = name()
    val futureScore = score()
    val futureFriends = friends()

    for {
        nameResult <- futureName
        scoreResult <- futureScore
        friendsResult <- futureFriends
    } yield {
        Profile(nameResult, scoreResult, friendsResult)
    }
}

futuresSetup.scala

def name(): Future[String] = Future { "david" }
def score(): Future[Double] = Future { 50.0 }
def friends(): Future[List[Int]] = Future { List(1, 2, 3) }

profile.scala

case class Profile(name: String, score: Double, friends: List[Int])

stateBad.scala

class MySQLStateService(private var nodes: Set[String]) {

    def getHealthyNodes(): Set[String] = nodes
  
    def updateState(node: String, status: Boolean) {
        if (status) nodes = nodes + node
        else nodes = nodes - node
    }

}

val state: MySQLStateService = {
    val service = new MySQLStateService(Set.empty)
    
    Zoo.on("/Health/MySQL/node1") {
        case NodeUpdated(value) if value == "UP" => state.updateState("node1", true)
        case _ => state.updateState("node1", false)
    }
  
    service
}

stateGood.scala

class MySQLStateService(private val agent: Agent[Set[String]]) {
  
    def getHealthyNodes(): Set[String] = agent.apply()

}

val service = {
    val agent: Agent[Set[String]] = Agent(Set.empty)
  
    Zoo.on("/Health/MySQL/node1") {
        case NodeUpdated(value) if value == "UP" => agent send (prev => prev  + "node1")
        case _ => agent send (prev => prev - "node1")
    }
  
    new MySQLStateService(agent)
}

zk.scala

import com.twitter.zookeeper.ZooKeeperClient

object Zoo {

    lazy val zk: ZooKeeperClient = ...
 
    def on(path: String)(callback: NodeStatusChange => Unit) = {
        zk watchNode (path, {
            (data: Option[Array[Byte]]) =>
                data match {
                    case Some(d) if d.isEmpty =>
                        callback(NodeUpdated(None))
                    case Some(d) =>
                        val value = new String(d)
                        callback(NodeUpdated(Option(value)))
                    case None =>
                        callback(NodeDeleted)
                }
        })
    }
}

Some.apply(x) does the same thing as Option.apply(x) but has a more restrictive type.