Скачать или смотреть Resolving IllegalStateException When Testing Spring + Kafka Embedded Multiple Consumers in a Group

Learn how to effectively test multiple consumers in the same Kafka group using Spring, avoiding rebalance-related exceptions while handling messages across partitions.
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Troubleshooting Parallel Consumption in Spring and Kafka

Testing a Spring application integrated with Kafka can sometimes result in frustrating errors. One such common error is the IllegalStateException occurring when trying to set up multiple consumers for a partitioned topic. In this post, we will examine how to troubleshoot and resolve this issue when testing multiple consumers in a group.

Understanding the Problem

When you configure multiple consumers to consume messages from a Kafka topic with multiple partitions, you might expect that each consumer would receive messages without any issues. However, you may encounter the following exception:

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Prior to this error, you might see numerous logs indicating that the consumer group is already rebalancing. This arises due to Kafka’s mechanism to manage group membership, leading to failures when multiple consumers try to join the same group and poll messages simultaneously.

Why Does This Happen?

The core of this problem lies in how the Kafka consumer group manages partition assignment. Kafka is designed to provide one consumer per partition within a consumer group in order to guarantee that each message is processed exactly once. When trying to use multiple consumers, the rebalancing logic can lead to the error you experienced.

Solution Overview

To resolve this IllegalStateException, we suggest the following steps:

Manual Assignment of Partitions

Adjustment of Consumer Configuration

Ensuring Proper Messaging Logic in Tests

Step 1: Manual Assignment of Partitions

Instead of relying on Kafka’s automatic management and group coordination, manually assign the partitions to each consumer. Replace this line of code:

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with:

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In this case, ensure that you maintain track of partition so each consumer grabs a unique partition.

Step 2: Consumer Configuration Adjustments

To facilitate better communication between the embedded Kafka broker and your Spring application, you need to set the correct bootstrap server property in your embedded Kafka configuration. Make sure to include the following line in your broker properties:

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This ensures that your Kafka template sends the records where they are supposed to go.

Step 3: Updating Your Test Logic

Your tests should produce messages that are distributed across the partitions deterministically. Here’s a refined example of your test method that ensures each consumer accurately processes its assigned partition:

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In this revised test, each message is sent to one of the three partitions based on the modulo of the i index. This method guarantees that records are properly divided among the consumers.

Conclusion

Handling multiple consumers with Kafka requires a special approach, particularly when working with tests in Spring. By using manual partition assignment, properly configuring your broker properties, and fine-tuning your test logic, you can effectively avoid common pitfalls like the IllegalStateException and ensure seamless message processing across your consumers.

If you have further queries or issues regarding Kafka consumer setups, feel free to explore the official documentation or share your questions in the community for assistance!