KafkaStreams 同一应用程序中的多个流

Question

我正在尝试根据 KafkaStreams 的惯例和合理性做出实用的设计决策。

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收听该主题的 KStream。

据我所知，我不能对使用 KafkaStreams 的消息使用条件转发，因此如果流订阅了多个主题（例如，一个用于上述消息中的每一个）我只能调用 stream.to 在单个接收器主题上 - 否则，我将不得不在流上调用 foreach 并将带有 KProducer 的消息发送到接收器主题。

以上建议使用单个流。我以为我可以在同一个应用程序中设置多个流，每个流听一个主题，映射并转发到 table 接收器，但每次我尝试创建 KafkaStreams 的两个实例时，只有第一个被初始化订阅它的主题 - 另一个从客户端收到警告，它的主题没有订阅。

我可以在同一个应用程序中设置多个流吗？如果可以，有什么特殊要求吗？

    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
    }

我也喜欢建议的任何替代方案

Answer 1

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

您知道 KStream#split()（KStream#branch() 顺序版本）吗？与条件转发基本相同

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

这应该按如下方式工作：

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

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

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。也许你可以分享你的代码？

Answer 2

当您创建 KafkaStreams 时，您需要使用不同的 application.id 传递属性，例如：

    props.put(StreamsConfig.APPLICATION_ID_CONFIG,"APP1");
    StreamsBuilder builder = new SteamsBuilder();
    KStream stream1 = builder.stream("topic1");
    KafkaStreams streams = new KafkaStreams(builder, props);
    streams.start();

然后你应该创建另一个流：

    props.put(StreamsConfig.APPLICATION_ID_CONFIG,"APP2");
    StreamsBuilder builder = new SteamsBuilder();
    KStream stream2 = builder.stream("topic2");
    KafkaStreams streams2 = new KafkaStreams(builder, props);
    streams2.start();

KafkaStreams 同一应用程序中的多个流

KafkaStreams multiple streams in same application

apache-kafka

apache-kafka-streams