在使用akka-typed的過程中發現有很多地方都簡化了不少，變得更方便了，包括：Supervision，只要用Behaviors.supervise()把Behavior包住，很容易就可以實現這個actor的SupervisorStrategy.restartWithBackoff策略了。然後叢集化的group router使用起來也很方便，再就是叢集分片cluster-sharding了。下面我們就通過一個例子來介紹cluster-sharding的具體使用方法。
首先，分片的意思是指在叢集中多個節點上部署某種actor，即entity，的構建機制。entity的構建是動態的，ClusterSharding系統根據各節點的負載情況決定到底在哪個節點構建entity，然後返回ShardRegion：一個該類entity具體的構建工具及訊息中介。也就是說我們可以把同樣的一種運算通過entityId指定給任何一個entity，但具體這個entity生存在叢集哪個節點上人工是無法確定的，完全靠ClusterSharding引導。先設計一個簡單功能的actor，測試它作為一個entity的工作細節：
object Counter {
sealed trait Command extends CborSerializable
case object Increment extends Command
final case class GetValue(replyTo: ActorRef[Response]) extends Command
case object StopCounter extends Command
private case object Idle extends Command
sealed trait Response extends CborSerializable
case class SubTtl(entityId: String, ttl: Int) extends Response
val TypeKey = EntityTypeKey[Command]("Counter")
def apply(nodeAddress: String, entityContext: EntityContext[Command]): Behavior[Command] = {
Behaviors.setup { ctx =>
def updated(value: Int): Behavior[Command] = {
Behaviors.receiveMessage[Command] {
case Increment =>
ctx.log.info("******************{} counting at {},{}",ctx.self.path,nodeAddress,entityContext.entityId)
updated(value + 1)
case GetValue(replyTo) =>
ctx.log.info("******************{} get value at {},{}",ctx.self.path,nodeAddress,entityContext.entityId)
replyTo ! SubTtl(entityContext.entityId,value)
Behaviors.same
case Idle =>
entityContext.shard ! ClusterSharding.Passivate(ctx.self)
Behaviors.same
case StopCounter =>
Behaviors.stopped(() => ctx.log.info("************{} stopping ... passivated for idling.", entityContext.entityId))
}
}
ctx.setReceiveTimeout(30.seconds, Idle)
updated(0)
}
}
}
cluster-sharding的機制是這樣的：在每個（或指定的）節點上構建部署一個某種EntityType的ShardRegion。這樣系統可以在任何部署了ShardRegion的節點上構建這種entity。然後ClusterSharding系統會根據entityId來引導訊息至正確的接收物件。我們再看看ShardRegion的部署是如何實現的吧：
object EntityManager {
sealed trait Command
case class AddOne(counterId: String) extends Command
case class GetSum(counterId: String ) extends Command
case class WrappedTotal(res: Counter.Response) extends Command
def apply(): Behavior[Command] = Behaviors.setup { ctx =>
val cluster = Cluster(ctx.system)
val sharding = ClusterSharding(ctx.system)
val entityType = Entity(Counter.TypeKey) { entityContext =>
Counter(cluster.selfMember.address.toString,entityContext)
}.withStopMessage(Counter.StopCounter)
sharding.init(entityType)
val counterRef: ActorRef[Counter.Response] = ctx.messageAdapter(ref => WrappedTotal(ref))
Behaviors.receiveMessage[Command] {
case AddOne(cid) =>
val entityRef: EntityRef[Counter.Command] = sharding.entityRefFor(Counter.TypeKey, cid)
entityRef ! Counter.Increment
Behaviors.same
case GetSum(cid) =>
val entityRef: EntityRef[Counter.Command] = sharding.entityRefFor(Counter.TypeKey, cid)
entityRef ! Counter.GetValue(counterRef)
Behaviors.same
case WrappedTotal(ttl) => ttl match {
case Counter.SubTtl(eid,subttl) =>
ctx.log.info("***********************{} total: {} ",eid,subttl)
}
Behaviors.same
}
}
}
太簡單了, sharding.ini(entityType)一個函式完成了一個節點分片部署。系統通過sharding.init(entityType)來實現ShardRegion構建。這個entityType代表某種特殊actor模版，看看它的構建函式：
object Entity {
/**
* Defines how the entity should be created. Used in [[ClusterSharding#init]]. More optional
* settings can be defined using the `with` methods of the returned [[Entity]].
*
* @param typeKey A key that uniquely identifies the type of entity in this cluster
* @param createBehavior Create the behavior for an entity given a [[EntityContext]] (includes entityId)
* @tparam M The type of message the entity accepts
*/
def apply[M](typeKey: EntityTypeKey[M])(
createBehavior: EntityContext[M] => Behavior[M]): Entity[M, ShardingEnvelope[M]] =
new Entity(createBehavior, typeKey, None, Props.empty, None, None, None, None, None)
}
這個函式需要一個EntityTyeKey和一個構建Behavior的函式createBehavior，產生一個Entity型別。Entity型別定義如下：
final class Entity[M, E] private[akka] (
val createBehavior: EntityContext[M] => Behavior[M],
val typeKey: EntityTypeKey[M],
val stopMessage: Option[M],
val entityProps: Props,
val settings: Option[ClusterShardingSettings],
val messageExtractor: Option[ShardingMessageExtractor[E, M]],
val allocationStrategy: Option[ShardAllocationStrategy],
val role: Option[String],
val dataCenter: Option[DataCenter]) {
/**
* [[akka.actor.typed.Props]] of the entity actors, such as dispatcher settings.
*/
def withEntityProps(newEntityProps: Props): Entity[M, E] =
copy(entityProps = newEntityProps)
/**
* Additional settings, typically loaded from configuration.
*/
def withSettings(newSettings: ClusterShardingSettings): Entity[M, E] =
copy(settings = Option(newSettings))
/**
* Message sent to an entity to tell it to stop, e.g. when rebalanced or passivated.
* If this is not defined it will be stopped automatically.
* It can be useful to define a custom stop message if the entity needs to perform
* some asynchronous cleanup or interactions before stopping.
*/
def withStopMessage(newStopMessage: M): Entity[M, E] =
copy(stopMessage = Option(newStopMessage))
/**
*
* If a `messageExtractor` is not specified the messages are sent to the entities by wrapping
* them in [[ShardingEnvelope]] with the entityId of the recipient actor. That envelope
* is used by the [[HashCodeMessageExtractor]] for extracting entityId and shardId. The number of
* shards is then defined by `numberOfShards` in `ClusterShardingSettings`, which by default
* is configured with `akka.cluster.sharding.number-of-shards`.
*/
def withMessageExtractor[Envelope](newExtractor: ShardingMessageExtractor[Envelope, M]): Entity[M, Envelope] =
new Entity(
createBehavior,
typeKey,
stopMessage,
entityProps,
settings,
Option(newExtractor),
allocationStrategy,
role,
dataCenter)
/**
* Allocation strategy which decides on which nodes to allocate new shards,
* [[ClusterSharding#defaultShardAllocationStrategy]] is used if this is not specified.
*/
def withAllocationStrategy(newAllocationStrategy: ShardAllocationStrategy): Entity[M, E] =
copy(allocationStrategy = Option(newAllocationStrategy))
/**
* Run the Entity actors on nodes with the given role.
*/
def withRole(newRole: String): Entity[M, E] = copy(role = Some(newRole))
/**
* The data center of the cluster nodes where the cluster sharding is running.
* If the dataCenter is not specified then the same data center as current node. If the given
* dataCenter does not match the data center of the current node the `ShardRegion` will be started
* in proxy mode.
*/
def withDataCenter(newDataCenter: DataCenter): Entity[M, E] = copy(dataCenter = Some(newDataCenter))
private def copy(
createBehavior: EntityContext[M] => Behavior[M] = createBehavior,
typeKey: EntityTypeKey[M] = typeKey,
stopMessage: Option[M] = stopMessage,
entityProps: Props = entityProps,
settings: Option[ClusterShardingSettings] = settings,
allocationStrategy: Option[ShardAllocationStrategy] = allocationStrategy,
role: Option[String] = role,
dataCenter: Option[DataCenter] = dataCenter): Entity[M, E] = {
new Entity(
createBehavior,
typeKey,
stopMessage,
entityProps,
settings,
messageExtractor,
allocationStrategy,
role,
dataCenter)
}
}
這裡面有許多方法用來控制Entity的構建和作業。
然後我們把這個EntityManager當作RootBehavior部署到多個節點上去：
object ClusterShardingApp {
def main(args: Array[String]): Unit = {
if (args.isEmpty) {
startup("shard", 25251)
startup("shard", 25252)
startup("shard", 25253)
startup("front", 25254)
} else {
require(args.size == 2, "Usage: role port")
startup(args(0), args(1).toInt)
}
}
def startup(role: String, port: Int): Unit = {
// Override the configuration of the port when specified as program argument
val config = ConfigFactory
.parseString(s"""
akka.remote.artery.canonical.port=$port
akka.cluster.roles = [$role]
""")
.withFallback(ConfigFactory.load("cluster"))
val entityManager = ActorSystem[EntityManager.Command](EntityManager(), "ClusterSystem", config)
...
}
一共設定了3個role=shard節點和1個front節點。
在front節點上對entityId分別為9013，9014，9015，9016幾個entity傳送訊息：
def startup(role: String, port: Int): Unit = {
// Override the configuration of the port when specified as program argument
val config = ConfigFactory
.parseString(s"""
akka.remote.artery.canonical.port=$port
akka.cluster.roles = [$role]
""")
.withFallback(ConfigFactory.load("cluster"))
val entityManager = ActorSystem[EntityManager.Command](EntityManager(), "ClusterSystem", config)
if (role == "front") {
entityManager ! EntityManager.AddOne("9013")
entityManager ! EntityManager.AddOne("9014")
entityManager ! EntityManager.AddOne("9013")
entityManager ! EntityManager.AddOne("9015")
entityManager ! EntityManager.AddOne("9013")
entityManager ! EntityManager.AddOne("9014")
entityManager ! EntityManager.AddOne("9014")
entityManager ! EntityManager.AddOne("9013")
entityManager ! EntityManager.AddOne("9015")
entityManager ! EntityManager.AddOne("9015")
entityManager ! EntityManager.AddOne("9016")
entityManager ! EntityManager.GetSum("9014")
entityManager ! EntityManager.GetSum("9015")
entityManager ! EntityManager.GetSum("9013")
entityManager ! EntityManager.GetSum("9016")
}
以下是部分運算結果顯示：
15:12:10.073 [ClusterSystem-akka.actor.default-dispatcher-15] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/786/9014 counting at akka://ClusterSystem@127.0.0.1:25253,9014 15:12:10.106 [ClusterSystem-akka.actor.default-dispatcher-15] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/786/9014 counting at akka://ClusterSystem@127.0.0.1:25253,9014 15:12:10.106 [ClusterSystem-akka.actor.default-dispatcher-15] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/786/9014 counting at akka://ClusterSystem@127.0.0.1:25253,9014 15:12:10.106 [ClusterSystem-akka.actor.default-dispatcher-3] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/785/9013 counting at akka://ClusterSystem@127.0.0.1:25251,9013 15:12:10.107 [ClusterSystem-akka.actor.default-dispatcher-3] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/785/9013 counting at akka://ClusterSystem@127.0.0.1:25251,9013 15:12:10.107 [ClusterSystem-akka.actor.default-dispatcher-3] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/785/9013 counting at akka://ClusterSystem@127.0.0.1:25251,9013 15:12:10.107 [ClusterSystem-akka.actor.default-dispatcher-3] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/785/9013 counting at akka://ClusterSystem@127.0.0.1:25251,9013 15:12:10.109 [ClusterSystem-akka.actor.default-dispatcher-19] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/787/9015 counting at akka://ClusterSystem@127.0.0.1:25254,9015 15:12:10.110 [ClusterSystem-akka.actor.default-dispatcher-19] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/787/9015 counting at akka://ClusterSystem@127.0.0.1:25254,9015 15:12:10.110 [ClusterSystem-akka.actor.default-dispatcher-19] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/787/9015 counting at akka://ClusterSystem@127.0.0.1:25254,9015 15:12:10.110 [ClusterSystem-akka.actor.default-dispatcher-19] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/787/9015 get value at akka://ClusterSystem@127.0.0.1:25254,9015 15:12:10.112 [ClusterSystem-akka.actor.default-dispatcher-18] INFO com.learn.akka.EntityManager$ - ***********************9015 total: 3 15:12:10.149 [ClusterSystem-akka.actor.default-dispatcher-15] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/786/9014 get value at akka://ClusterSystem@127.0.0.1:25253,9014 15:12:10.149 [ClusterSystem-akka.actor.default-dispatcher-3] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/785/9013 get value at akka://ClusterSystem@127.0.0.1:25251,9013 15:12:10.169 [ClusterSystem-akka.actor.default-dispatcher-18] INFO com.learn.akka.EntityManager$ - ***********************9014 total: 3 15:12:10.169 [ClusterSystem-akka.actor.default-dispatcher-18] INFO com.learn.akka.EntityManager$ - ***********************9013 total: 4 15:12:10.171 [ClusterSystem-akka.actor.default-dispatcher-3] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/788/9016 counting at akka://ClusterSystem@127.0.0.1:25251,9016 15:12:10.171 [ClusterSystem-akka.actor.default-dispatcher-3] INFO com.learn.akka.Counter$ - ******************akka://ClusterSystem/system/sharding/Counter/788/9016 get value at akka://ClusterSystem@127.0.0.1:25251,9016 15:12:10.172 [ClusterSystem-akka.actor.default-dispatcher-18] INFO com.learn.akka.EntityManager$ - ***********************9016 total: 1 15:19:32.176 [ClusterSystem-akka.actor.default-dispatcher-3] INFO com.learn.akka.Counter$ - ************9013 stopping ... passivated for idling. 15:19:52.529 [ClusterSystem-akka.actor.default-dispatcher-3] INFO com.learn.akka.Counter$ - ************9014 stopping ... passivated for idling. 15:19:52.658 [ClusterSystem-akka.actor.default-dispatcher-3] INFO com.learn.akka.Counter$ - ************9016 stopping ... passivated for idling. 15:19:52.662 [ClusterSystem-akka.actor.default-dispatcher-14] INFO com.learn.akka.Counter$ - ************9015 stopping ... passivated for idling.
下面是本次示範的完整原始碼：
ClusterSharding.scala
package com.learn.akka import scala.concurrent.duration._ import akka.actor.typed._ import akka.actor.typed.scaladsl._ import akka.cluster.sharding.typed.scaladsl.EntityContext import akka.cluster.sharding.typed.scaladsl.Entity import akka.persistence.typed.PersistenceId //#sharding-extension import akka.cluster.sharding.typed.ShardingEnvelope import akka.cluster.sharding.typed.scaladsl.ClusterSharding import akka.cluster.sharding.typed.scaladsl.EntityTypeKey import akka.cluster.sharding.typed.scaladsl.EntityRef import com.typesafe.config.ConfigFactory import akka.cluster.typed.Cluster //#counter object Counter { sealed trait Command extends CborSerializable case object Increment extends Command final case class GetValue(replyTo: ActorRef[Response]) extends Command case object StopCounter extends Command private case object Idle extends Command sealed trait Response extends CborSerializable case class SubTtl(entityId: String, ttl: Int) extends Response val TypeKey = EntityTypeKey[Command]("Counter") def apply(nodeAddress: String, entityContext: EntityContext[Command]): Behavior[Command] = { Behaviors.setup { ctx => def updated(value: Int): Behavior[Command] = { Behaviors.receiveMessage[Command] { case Increment => ctx.log.info("******************{} counting at {},{}",ctx.self.path,nodeAddress,entityContext.entityId) updated(value + 1) case GetValue(replyTo) => ctx.log.info("******************{} get value at {},{}",ctx.self.path,nodeAddress,entityContext.entityId) replyTo ! SubTtl(entityContext.entityId,value) Behaviors.same case Idle => entityContext.shard ! ClusterSharding.Passivate(ctx.self) Behaviors.same case StopCounter => Behaviors.stopped(() => ctx.log.info("************{} stopping ... passivated for idling.", entityContext.entityId)) } } ctx.setReceiveTimeout(30.seconds, Idle) updated(0) } } } object EntityManager { sealed trait Command case class AddOne(counterId: String) extends Command case class GetSum(counterId: String ) extends Command case class WrappedTotal(res: Counter.Response) extends Command def apply(): Behavior[Command] = Behaviors.setup { ctx => val cluster = Cluster(ctx.system) val sharding = ClusterSharding(ctx.system) val entityType = Entity(Counter.TypeKey) { entityContext => Counter(cluster.selfMember.address.toString,entityContext) }.withStopMessage(Counter.StopCounter) sharding.init(entityType) val counterRef: ActorRef[Counter.Response] = ctx.messageAdapter(ref => WrappedTotal(ref)) Behaviors.receiveMessage[Command] { case AddOne(cid) => val entityRef: EntityRef[Counter.Command] = sharding.entityRefFor(Counter.TypeKey, cid) entityRef ! Counter.Increment Behaviors.same case GetSum(cid) => val entityRef: EntityRef[Counter.Command] = sharding.entityRefFor(Counter.TypeKey, cid) entityRef ! Counter.GetValue(counterRef) Behaviors.same case WrappedTotal(ttl) => ttl match { case Counter.SubTtl(eid,subttl) => ctx.log.info("***********************{} total: {} ",eid,subttl) } Behaviors.same } } } object ClusterShardingApp { def main(args: Array[String]): Unit = { if (args.isEmpty) { startup("shard", 25251) startup("shard", 25252) startup("shard", 25253) startup("front", 25254) } else { require(args.size == 2, "Usage: role port") startup(args(0), args(1).toInt) } } def startup(role: String, port: Int): Unit = { // Override the configuration of the port when specified as program argument val config = ConfigFactory .parseString(s""" akka.remote.artery.canonical.port=$port akka.cluster.roles = [$role] """) .withFallback(ConfigFactory.load("cluster")) val entityManager = ActorSystem[EntityManager.Command](EntityManager(), "ClusterSystem", config) if (role == "front") { entityManager ! EntityManager.AddOne("9013") entityManager ! EntityManager.AddOne("9014") entityManager ! EntityManager.AddOne("9013") entityManager ! EntityManager.AddOne("9015") entityManager ! EntityManager.AddOne("9013") entityManager ! EntityManager.AddOne("9014") entityManager ! EntityManager.AddOne("9014") entityManager ! EntityManager.AddOne("9013") entityManager ! EntityManager.AddOne("9015") entityManager ! EntityManager.AddOne("9015") entityManager ! EntityManager.AddOne("9016") entityManager ! EntityManager.GetSum("9014") entityManager ! EntityManager.GetSum("9015") entityManager ! EntityManager.GetSum("9013") entityManager ! EntityManager.GetSum("9016") } } }
cluster.conf
akka { actor { provider = cluster serialization-bindings { "com.learn.akka.CborSerializable" = jackson-cbor } } remote { artery { canonical.hostname = "127.0.0.1" canonical.port = 0 } } cluster { seed-nodes = [ "akka://ClusterSystem@127.0.0.1:25251", "akka://ClusterSystem@127.0.0.1:25252"] } }