KafkaStreams在同一应用程序中多个流 [英] KafkaStreams multiple streams in same application

问题描述

我正在尝试根据惯例和KafkaStreams的合理性做出切实可行的设计决策.

I'm trying to make a practical design decision based on convention and plausibility with KafkaStreams.

假设我有两个不同的事件要放入 KTable 中.我有一个生产者，将这些消息发送到正在监听该主题的 KStream 中.

Let's say that I have two different events that I want to place into KTables. I have a producer sending these messages to a KStream that is listening to that topic.

据我所知，我不能对使用 KafkaStreams 的消息使用条件转发，因此，如果流订阅了许多主题(例如，上述消息中的每一个)，则我只能调用在单个接收器主题上使用 stream.to -否则，我将不得不在流上执行诸如调用 foreach 的操作，并使用 KProducer 发送消息接收器主题.

From what I can tell I cannot use conditional forwarding for messages using KafkaStreams, so if the stream is subscribe to many topics (one for each of the above messages, for example) I can only call stream.to on a single sink topic - otherwise, I would have to do something like call foreach on the stream and send messages with a KProducer to the sink topics.

以上建议使用单个流.我以为可以在同一个应用程序中设置多个流，每个流都监听一个主题，映射并转发到表接收器，但是每次我尝试创建两个 KafkaStreams 实例时，只有第一个初始化的订阅到其主题-另一个从客户端收到警告，其主题没有订阅.

The above suggests using a single stream. I thought I could set up multiple streams in the same app, each listening to a topic, mapping and forwarding to a table sink, but everytime I try to create two instances of KafkaStreams, only the first initialized subscribes to its topic - the other gets a warning from the client that its topic has no subscriptions.

我可以在同一个应用中设置多个流吗?如果是这样，有什么特殊要求吗?

Can I set up multiple streams in the same app? If so, are there any special requirements?

class Stream(topic: String) {
  val props: Option[Map[String, String]] = Some(TopicProps.get(topic))
  val streamsBuilder = new StreamsBuilder
  val topics = new util.ArrayList[String]
  topics.add(props.get("topic"))

  val stream: KStream[String, String] = configureStream(streamsBuilder, topics, props.get("sink"))

  def configureStream(builder: StreamsBuilder, topics: java.util.List[String], sink: String): KStream[String, String] = {
    builder.stream[String, String](
      topics,
      Consumed.`with`(String(), String())
    )
  }

  def init(): KafkaStreams = {
    val streams = new KafkaStreams(streamsBuilder.build(), KafkaConfig.streamConfig)

    streams.start()

    streams
  }
}

class Streams() {

  val eventStream = new Stream("first_event") //looking good!
  val eventStream2 = new Stream("second_event") // no subscribers
  //if I switch the other of these, eventStream2 is subscribed to and eventStream is dead in the water
  val streams: KafkaStreams = eventStream.init()
  val streams2: KafkaStreams = eventStream2.init()

}

流配置

val streamConfig: Properties = {
    val properties = new Properties()
    properties.put(StreamsConfig.APPLICATION_ID_CONFIG, "stream-application")
    properties.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, BrokerHost)
    properties
}

我也很喜欢建议的其他选择

I'd also love any alternatives suggested

推荐答案

据我所知，我不能对消息使用条件转发

From what I can tell I cannot use conditional forwarding for messages

您了解 KStream#branch()吗?基本上与条件转发相同.

Do you know about KStream#branch()? It basically the same as conditional forwarding.

我以为我可以在同一个应用中设置多个流，每个流都监听一个主题，映射并转发到表接收器，

I thought I could set up multiple streams in the same app, each listening to a topic, mapping and forwarding to a table sink,

这应该如下工作:

StreamsBuilder builder = new SteamsBuilder();
KStream stream1 = builder.stream("topic1");
KStream stream2 = builder.stream("topic2");

stream1.to("table1-topic");
stream2.to("table2-topic");

但是每次我尝试创建两个KafkaStreams实例时，只有第一个初始化的实例订阅了它的主题-另一个则从客户端收到一条警告，表明其主题没有订阅.

but everytime I try to create two instances of KafkaStreams, only the first initialized subscribes to its topic - the other gets a warning from the client that its topic has no subscriptions.

不确定.这应该工作.也许您可以共享您的代码?

Not sure. This should work. Maybe you can share your code?

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