Exploring EmbeddedKafka and KafkaContainers in Spring Boot

Apache Kafka has become a pivotal component in modern software development for building distributed event driven and streaming applications. When working with Kafka in a Spring Boot application, developers often have the choice between using EmbeddedKafka and KafkaContainers for integration testing. These tools serve similar purposes but have distinct characteristics and use cases. In this article, we will delve into the differences between EmbeddedKafka and KafkaContainers in the context of Spring Boot applications.

EmbeddedKafka

EmbeddedKafka is part of the Spring Kafka testing library and provides an in-memory, lightweight Kafka broker. It’s an excellent choice for unit and integration tests because it allows you to run Kafka within the JVM process of your test, avoiding the need for external Kafka infrastructure.

Key Features

1. In-Memory Kafka broker: EmbeddedKafka creates an in-memory Kafka broker for testing purposes, which helps ensure test isolation and eliminates external dependencies.
2. Simple setup: Setting up EmbeddedKafka is straightforward, making it a great choice for unit testing Kafka-related functionality.
3. Spring integration: It integrates seamlessly with the Spring ecosystem, making it well-suited for Spring Boot applications.
4. Configurability: You can configure EmbeddedKafka to mimic a production Kafka setup by specifying properties like the number of partitions and replication factors.
5. Fast testing: Tests typically run faster because there’s no network overhead associated with connecting to an external Kafka cluster.

Drawbacks

1. Limited realism: Embedded Kafka might not perfectly mimic the behaviour of a full Kafka cluster, potentially missing certain nuances.
2. Resource intensive: Running multiple instances of Embedded Kafka can consume significant memory and CPU resources, especially for larger test suites.

Use Cases

• Unit testing: EmbeddedKafka is a good choice for testing individual components that interact with Kafka in isolation, without involving a running Kafka cluster.
• Integration testing: It’s suitable for lightweight integration tests where a full Kafka cluster isn’t necessary.

KafkaContainers

Kafka Containers, on the other hand, use containerisation technology to run Kafka in a Docker container. KafkaContainers is part of the Testcontainers project, which provides Docker-based containers for testing various services. Testcontainers is a library that manages container lifecycles during testing, including Kafka containers. KafkaContainers allows you to run a real Kafka broker in a Docker container, providing a more production-like environment for testing.

Key Features

1. Dockerised Kafka: KafkaContainers runs Kafka inside a Docker container, making it closer to a real Kafka deployment than `EmbeddedKafka`.
2. Test isolation: Docker containers are isolated, so tests won’t interfere with each other, ensuring a more reliable testing environment.
3. Realistic testing: It’s a good choice for more realistic integration tests, especially when you want to test your application’s behaviour against an actual Kafka cluster configuration.
4. Compatibility: Since it uses real Kafka, it’s suitable for testing scenarios that involve advanced Kafka features, custom configurations, or complex network setups.
5. Environment consistency: It ensures consistency between your development, testing, and production environments, as you are using the same Kafka distribution and configuration.

Drawbacks

1. Complexity: Setting up and configuring Kafka Containers can be a little more complex compared to Embedded Kafka. It needs Docker to be started in the background.
2. Slower testing: Tests that rely on Kafka Containers might run slower due to network latency and container initialisation.

Use Cases

• Integration testing: KafkaContainers is ideal when you need to test your Spring Boot application against a full-fledged Kafka cluster, especially when you want to validate the behaviour of your application under various real-world Kafka configurations.
• End-to-end testing: It’s useful for end-to-end testing scenarios where your application interacts with Kafka as part of a larger system.

Choosing between EmbeddedKafka and KafkaContainers

The choice between EmbeddedKafka and KafkaContainers depends on your specific testing requirements:

• If you need lightweight, fast-running tests with simple Kafka interactions, EmbeddedKafka is a good choice.
• If you require more complex integration testing with a production-like Kafka environment, including testing advanced Kafka features and configurations, KafkaContainers is the better option. In practice, some projects may use both tools for different testing scenarios, combining the benefits of simplicity and realism in their testing strategies. Ultimately, your choice should align with the specific needs of your Spring Boot application and your testing objectives.

Conclusion

In summary, EmbeddedKafka and KafkaContainers are both valuable tools for testing Kafka-related functionality in Spring Boot applications. They offer different trade-offs between simplicity and realism, allowing you to choose the one that best suits your testing needs. Are you still unsure which Kafka setup is best for your Spring Boot project, or do you have more questions about using Kafka in your applications? Feel free to contact us for personalised guidance or further information. We have experts that can assist you in making the right choice for your specific needs.