Скачать или смотреть Resolving the Kafka Listener Issue: Why Your Kafka Listener Isn't Listening

Struggling with a Kafka consumer in Java that doesn't seem to be listening? Let's dissect the problem and uncover the likely cause: a missing SSL property in your configuration.
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This video is based on the question https://stackoverflow.com/q/62818594/ asked by the user 'JeyJ' ( https://stackoverflow.com/u/4340793/ ) and on the answer https://stackoverflow.com/a/62891321/ provided by the user 'JeyJ' ( https://stackoverflow.com/u/4340793/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Kafka Listener Problem

If you've ever faced the frustrating issue of a Kafka listener seemingly non-responsive, you're not alone. Many developers encounter this problem, where the Kafka consumer appears to be set up correctly yet does not receive messages. This post aims to clarify the reasons behind this behavior and provide a concrete solution to get your listener working effectively.

The Problem

You're using Java 11 and the kafka-client version 2.0.0 to create a Kafka consumer, and your log reveals that while the consumer is created and subscribed, it's not delivering records. Here’s a summary of your experience:

Your consumer runs in a polling loop but repeatedly logs that it's polling zero records.

There are no logs relating to partition assignment, and despite correct configuration values, the expected behavior is absent.

Key Pieces of Information

Java version: 11

Kafka client version: 2.0.0

Log outputs confirmed creation and subscription but no assignment activity.

You successfully tested with the kafka-console-consumer pointing to the correct topic.

Your configuration includes group.id, but lacks the necessary SSL properties.

Diagnosing the Issue

It turns out that the core of the issue revolves around the connectivity settings of your Kafka consumer. The key point you need to focus on is the SSL configuration.

Identifying the Cause

While it may seem that everything is correct at first glance, the fact that your listener never receives partition assignments suggests an issue with the security settings in your properties file.

What to Check

Properties Configuration: Ensure that your properties file contains all necessary configurations.

Security Protocol: Most importantly, if your Kafka broker is operating under SSL, you must specify this in your consumer properties.

The Solution: Adding the SSL Property

To rectify the listener issue, you should include the following property in your consumer configuration:

[[See Video to Reveal this Text or Code Snippet]]

Why Is This Important?

If your Kafka setup requires SSL and you don't inform the kafka-client API with the proper parameter, it will not throw an exception. This can lead to silent failures where the consumer cannot establish a secure connection, thus not receiving any messages from the Kafka topics.

Step-by-Step Implementation

Edit Your Configuration File:

Open the properties file you’re using to configure your Kafka consumer.

Add the line security.protocol=ssl.

Validate All Required Properties:

Ensure that your properties file contains all other necessary parameters, such as:

bootstrap.servers

group.id

key.deserializer

value.deserializer

Restart Your Consumer:

After making these changes, restart your Kafka consumer application.

Monitor the logs for any partition assignments and processed records.

Conclusion

By simply adding the security.protocol=ssl property to your Kafka consumer's configuration, you can solve the frustrating issue of listeners not responding. This fundamental aspect is often overlooked but is critical for establishing a successful connection to your Kafka broker, especially in a security-focused environment.

Now, get back to enjoying the seamless messaging delivery that Kafka is designed for—happy coding!