Definition

Kafka Single Message Transforms (SMTs) are lightweight, in-flight transformations applied to individual messages as they flow through Kafka Connect. These transformations can be applied to messages produced by source connectors before they are written to Kafka, or to messages consumed by sink connectors before they are sent to their final destination.

Common Use Cases

SMTs are versatile and can be used in various scenarios, including:

1. Field Renaming: Changing the names of fields in a message to match the schema expected by downstream systems.
2. Masking Values: Hiding sensitive information by masking certain fields.
3. Routing Records: Directing messages to different topics based on their content.
4. Timestamp Conversion: Adding or converting timestamps in messages.
5. Key Manipulation: Setting or modifying the key of a message based on its content.

Pros and Cons

Pros:

• Flexibility: SMTs provide a flexible way to manipulate messages without needing to modify the source or sink systems.
• Simplicity: They are easy to configure and use, often requiring just a few lines of configuration.
• Efficiency: SMTs operate in-flight, meaning they don’t add significant latency to message processing.

Cons:

• Limited Scope: SMTs are designed for lightweight transformations and may not be suitable for complex processing.
• Performance Overhead: While generally efficient, extensive use of SMTs can introduce some performance overhead.
• Debugging Challenges: Debugging issues related to SMTs can be challenging, especially in complex data pipelines.

Example: Logging a Message

Here’s an example of an SMT configuration that logs the content of each message:

In this example, the Log transform is used to log each message’s value to a file6.

Conclusion

Kafka SMTs are a powerful tool for performing lightweight, in-flight transformations on messages as they pass through Kafka Connect. They offer flexibility and simplicity, making them ideal for a variety of use cases, from field renaming to message routing. However, they are best suited for simple transformations and can introduce some performance overhead if overused.

Key Takeaways

• Definition: SMTs are in-flight transformations applied to individual messages in Kafka Connect.
• Use Cases: Common uses include field renaming, masking values, routing records, timestamp conversion, and key manipulation.
• Pros and Cons: SMTs are flexible and simple but have limited scope and can introduce performance overhead.
• Example: An SMT can be configured to log messages, providing visibility into message content as it flows through the system.

Custom SMT Code Example

First, create a new Java class for your custom SMT:

Steps to Use the Custom SMT

1. Compile the Code: Compile the Java class and package it into a JAR file.
2. Deploy the JAR: Copy the JAR file to the Kafka Connect plugin path.
3. Configure the Connector: Update your Kafka Connect configuration to use the custom SMT.

Example Configuration

Here’s how you can configure a Kafka Connect connector to use the custom SMT:

 In this configuration, the MaskEmail transform is applied to each message, masking any email addresses found in the message content.

Conclusion

Creating a custom SMT in Kafka Connect allows you to tailor message transformations to your specific needs. This example demonstrates how to mask sensitive information, but the possibilities are vast. Custom SMTs can help you ensure data privacy, format consistency, and more.

Key Takeaways

• Custom SMTs: Allow for tailored message transformations in Kafka Connect.
• Example: The provided code masks email addresses in messages.

Configuration: Custom SMTs are easy to integrate into Kafka Connect configurations.