Kafka pollable consumers lose ConsumerFactory listeners when max.poll.records is greater than one

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55/100
Issue-Typ
Bug
Klarheit
Größtenteils klar
Aktivitätsstatus
Aktiv
Tech-Stack
java, kafka, spring
Bereich
backend, distributed-systems, observability

Rechercherichtung

Start by reading Spring Integration Kafka's KafkaMessageSource, where the issue says a replacement DefaultKafkaConsumerFactory is created when max.poll.records is missing or greater than 1. Check how that replacement handles the original factory's listeners, then run the linked reproducer's SpringCloudStreamPollableKafkaMetricsTests to compare the two configurations. Done means the listener is preserved and native kafka.consumer.* meters register with either setting.

Vom Indexierungsmodell aus dem Issue-Text verfasst.

Beschreibung

Thanks for considering raising a Spring Cloud Stream issue.

Describe the issue
Kafka pollable consumers lose ConsumerFactory.Listener instances when max.poll.records is not set to 1.

This prevents Micrometer native Kafka metrics from being registered for the consumer created by KafkaMessageSource.

The issue is visible through Spring Cloud Stream, but the suspected root cause appears to be in Spring Integration Kafka's KafkaMessageSource.

To Reproduce
The issue can be reproduced with this standalone demo application:

https://github.com/ferblaca/demoStreamPollable

The reproducer uses:

  • Spring Boot 4.1.2;
  • Spring Cloud Stream 5.0.4;
  • the Spring Cloud Stream Kafka binder;
  • a real Kafka broker started with Testcontainers;
  • two Spring Cloud Stream pollable consumers.

Steps:

  1. Clone the repository:

    git clone https://github.com/ferblaca/demoStreamPollable.git
cd demoStreamPollable

  2. Run the reproducer test:

    ./mvnw -B -Dtest=SpringCloudStreamPollableKafkaMetricsTests test

  3. Review the test implementation:

    src/test/java/com/example/demoStreamPollable/SpringCloudStreamPollableKafkaMetricsTests.java

  4. The test creates two pollable bindings:

    pollableInput-in-0
pollableInputMaxOne-in-0

  5. The first binding is configured with:

    spring.cloud.stream.kafka.bindings.pollableInput-in-0.consumer.configuration.max.poll.records=10

    The test publishes and consumes a real Kafka message through PollableMessageSource, then verifies that no meter whose name starts with kafka.consumer is registered.

  6. The second binding is configured with:

    spring.cloud.stream.kafka.bindings.pollableInputMaxOne-in-0.consumer.configuration.max.poll.records=1

    The test publishes and consumes another real Kafka message through a second PollableMessageSource, then verifies that a meter whose name starts with kafka.consumer is registered.

The test passes and demonstrates the different behavior between both configurations.

Version of the framework

  • Spring Boot 4.1.2
  • Spring Cloud Stream 5.0.4
  • Java 25
  • Kafka broker: Testcontainers apache/kafka-native:3.8.0

Expected behavior
When KafkaMessageSource creates a replacement consumer factory, it should preserve the behavior of the supplied factory, including registered ConsumerFactory.Listener instances such as:

MicrometerConsumerListener

Native kafka.consumer.* metrics should be registered regardless of whether max.poll.records is explicitly set to 1.

Screenshots
Not applicable.

Additional context
Spring Cloud Stream's Kafka binder creates the consumer factory and invokes the registered ClientFactoryCustomizer before creating the pollable source.

The relevant flow is:

KafkaMessageChannelBinder
  -> createPolledConsumerResources(...)
  -> createKafkaConsumerFactory(...)
  -> ClientFactoryCustomizer.configure(consumerFactory)
  -> new KafkaMessageSource<>(consumerFactory, consumerProperties)

The customizer adds a MicrometerConsumerListener to the original DefaultKafkaConsumerFactory.

However, when max.poll.records is missing or greater than 1, KafkaMessageSource forces it to 1 by creating a new DefaultKafkaConsumerFactory.

The replacement factory copies the configuration and deserializers, but does not copy the listeners from the original factory. Consequently, the MicrometerConsumerListener is lost before the actual Kafka consumer is created.

The current behavior also logs:

max.poll.records' has been forced from 10 to 1, to avoid having to seek after each record

As a workaround, applications can configure max.poll.records=1 for each pollable Kafka binding. This prevents KafkaMessageSource from creating the replacement factory, but it exposes an internal implementation detail to applications.

Could you please confirm whether this issue should be fixed in:

  • Spring Integration Kafka, in KafkaMessageSource;
  • Spring Cloud Stream's Kafka binder;
  • or both?

The suspected fix is to copy the ConsumerFactory.Listener instances when KafkaMessageSource creates the replacement DefaultKafkaConsumerFactory. The reproducer is intentionally implemented through Spring Cloud Stream so that the behavior can be verified using a real PollableMessageSource and the Kafka binder, but the suspected defect appears to belong to Spring Integration Kafka.

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