AKKA 集群中的发布与订阅Distributed Publish Subscribe in Cluster

Distributed Publish Subscribe in Cluster

基本定义

在单机环境下订阅与发布是很常用的，然而在集群环境是比较麻烦和不好实现的；

AKKA已经提供了相应的实现，集群环境各节点之间的actor相互订阅发布感兴的主题的消息，

关键依赖媒介actor: akka.cluster.pubsub.DistributedPubSubMediator

订阅：

DistributedPubSubMediator.Subscribe方法将actor注册到本地中介者。
成功的订阅和取消订阅由DistributedPubSubMediator.SubscribeAck和DistributedPubSubMediator.UnsubscribeAck应答确认。这个确认消息意味着订阅已经注册了，但是它仍然需要花费一些时间复制到其它的节点上。节点之间发现与注册会有一定延迟，可能造成消息不会立即送达！

发布：

你通过向本地的中介者发送DistributedPubSubMediator.Publish消息来发布消息。
当actor终止时，它们会自动从注册表移除，或者你可以明确的使用DistributedPubSubMediator.Unsubscribe移除。

实现示例

package pubsub

import akka.actor.AbstractActor
import akka.actor.ActorRef
import akka.actor.ActorSystem
import org.slf4j.LoggerFactory
import scala.PartialFunction
import scala.runtime.BoxedUnit
import akka.cluster.pubsub.DistributedPubSubMediator
import akka.actor.Nobody.tell
import akka.actor.Props
import java.time.Clock.system
import akka.cluster.pubsub.DistributedPubSub
import akka.actor.Nobody.tell
import com.typesafe.config.ConfigFactory

/**
 * Created by: tankx
 * Date: 2019/7/16
 * Description: 发布订阅模式
 */
/**
 * 定义发布者
 */
class Pub() : AbstractActor() {

    private var log = LoggerFactory.getLogger(Pub::class.java)

    var mediator: ActorRef = DistributedPubSub.get(context.system).mediator()

    override fun createReceive(): Receive {
        return receiveBuilder().matchAny(this::receive).build()
    }

    private fun receive(msg: Any) {

        log.info("派发事件:$msg")
        if (msg is String) {
            mediator.tell(DistributedPubSubMediator.Publish(topA, msg), self)
        }

    }

}

/**
 * 定义订阅者
 */
class Sub() : AbstractActor() {

    private var log = LoggerFactory.getLogger(Sub::class.java)

    override fun preStart() {
        //注册订阅
        var mediator = DistributedPubSub.get(getContext().system()).mediator()
        mediator.tell(DistributedPubSubMediator.Subscribe(topA, self), self)

        println("注册订阅")
        //ActorRef.noSender()不会接收订阅信息DistributedPubSubMediator.SubscribeAck
        //mediator.tell(DistributedPubSubMediator.Subscribe(topA, self), ActorRef.noSender())

        //移除订阅
        //DistributedPubSub.get(getContext().system()).mediator().tell(DistributedPubSubMediator.Unsubscribe(topA, self), ActorRef.noSender())
    }

    override fun createReceive(): Receive {
        return receiveBuilder().matchAny(this::receive).build()
    }

    private fun receive(msg: Any) {

        when (msg) {
            is String -> log.info("收到事件: $msg")
            is DistributedPubSubMediator.SubscribeAck -> log.info("订阅事件:$msg")
            else -> log.info("无对应类型")
        }

    }

}

//定义主题
var topA: String = "topa"

fun getSystem(port: Int): ActorSystem {

    val config = ConfigFactory.parseString(
        "akka.remote.netty.tcp.port=$port"
    ).withFallback(
        ConfigFactory.load("application_pub.conf")
    )

    var actorSystem = ActorSystem.create("custerPubSystem", config);

    return actorSystem
}

fun main() {

    var system = getSystem(3660);

    var subActor = system.actorOf(Props.create(Sub::class.java))
    Thread.sleep(1000)//让sub 完全起来

//    var pubActor = system.actorOf(Props.create(Pub::class.java))
//    pubActor.tell("hello", ActorRef.noSender())
//
//    pubActor.tell("world", ActorRef.noSender())
//
//    Thread.sleep(3000)

}

上面订阅启动后，再启动一个节点派发事件

package pubsub

import akka.actor.ActorRef
import akka.actor.Props
import akka.cluster.pubsub.DistributedPubSub
import akka.cluster.pubsub.DistributedPubSubMediator

/**
 * Created by: tankx
 * Date: 2019/7/18
 * Description:
 */
fun main() {

    var system = getSystem(3661);

    Thread.sleep(3000)

    var mediator: ActorRef = DistributedPubSub.get(system).mediator()
　　
    for (i in 1..1000) {
        mediator.tell(DistributedPubSubMediator.Publish(topA, "消息XXXXXX"), ActorRef.noSender())

        Thread.sleep(2000)
    }

}

配置文件

akka {
  actor {
    provider = "akka.cluster.ClusterActorRefProvider"
  }

  cluster {
    seed-nodes = [
      "akka.tcp://custerPubSystem@127.0.0.1:3660"
    ]
  }

  remote {
    enabled-transports = ["akka.remote.netty.tcp"]
    netty.tcp {
      hostname = "127.0.0.1"
      port = 0
    }
  }

}

依赖JAR

    compile("com.typesafe.akka:akka-actor_2.13:$akkaVersion")
    compile("com.typesafe.akka:akka-remote_2.13:$akkaVersion")
    compile("com.typesafe.akka:akka-cluster-tools_2.13:$akkaVersion")

结果：

2019-07-18 20:19:55.941 [custerPubSystem-akka.actor.default-dispatcher-4] INFO  pubsub.Sub 77- 收到事件: 消息XXXXXX
2019-07-18 20:19:55.942 [custerPubSystem-akka.actor.default-dispatcher-4] INFO  pubsub.Sub 77- 收到事件: 消息XXXXXX

结论：

AKKA 集群中的发布与订阅在节点之间的Actor之间广播消息，监听自己关心的主题消息做相应逻辑，是非常方便与很多场景适用的