Advanced Kafka Custom Connect Plugins

Introduction to Kafka Connect

Apache Kafka Connect is a tool for integrating Kafka with external systems such as databases, key-value stores, and file systems. It provides a scalable and fault-tolerant way to stream data between Kafka and other systems using connectors.

Connectors in Kafka Connect can be either source connectors, which pull data from external systems into Kafka, or sink connectors, which push data from Kafka into external systems. Kafka Connect also supports custom connectors for specific use cases.

Why Create Custom Connect Plugins?

While Kafka Connect provides a variety of built-in connectors, there are scenarios where custom connectors are needed. These scenarios might include:

Creating a Custom Kafka Connect Plugin

Creating a custom Kafka Connect plugin involves several steps. Here is a high-level overview:

  1. Define the connector: Create a class that implements the SourceConnector or SinkConnector interface depending on whether you are building a source or sink connector.
  2. Implement the configuration: Define a configuration class that extends AbstractConfig to specify the configuration parameters for your connector.
  3. Implement the task: Create a class that implements SourceTask or SinkTask, responsible for the actual data transfer.
  4. Package and deploy: Package your plugin as a JAR file and place it in the Kafka Connect plugins directory.

Example Code for a Custom Kafka Connect Plugin

Below is an example of a custom Kafka Connect source connector that reads data from a hypothetical data source.


import org.apache.kafka.connect.source.SourceConnector;
import org.apache.kafka.connect.source.SourceTask;
import org.apache.kafka.connect.connector.Task;
import org.apache.kafka.connect.connector.Connector;
import org.apache.kafka.common.config.ConfigDef;
import org.apache.kafka.connect.connector.ConnectorContext;
import org.apache.kafka.connect.source.SourceRecord;
import java.util.List;
import java.util.Map;

public class CustomSourceConnector extends SourceConnector {
    private String configValue;

    @Override
    public void start(Map props) {
        configValue = props.get("config.key");
    }

    @Override
    public Class taskClass() {
        return CustomSourceTask.class;
    }

    @Override
    public List> taskConfigs(int maxTasks) {
        // Return task configurations here
        return null;
    }

    @Override
    public void stop() {
        // Clean up resources here
    }

    @Override
    public ConfigDef config() {
        return new ConfigDef()
            .define("config.key", ConfigDef.Type.STRING, "default", ConfigDef.Importance.HIGH, "Configuration Key");
    }

    @Override
    public String version() {
        return "1.0";
    }
}

public class CustomSourceTask extends SourceTask {
    @Override
    public void start(Map props) {
        // Initialize task here
    }

    @Override
    public List poll() throws InterruptedException {
        // Poll data from the data source and return SourceRecords
        return null;
    }

    @Override
    public void stop() {
        // Clean up resources here
    }

    @Override
    public String version() {
        return "1.0";
    }
}

In this example, CustomSourceConnector is the connector class that defines configuration and tasks, while CustomSourceTask implements the logic for polling data from the source.

Packaging and Deploying Your Custom Plugin

Once your custom connector and task classes are implemented, package them into a JAR file. This JAR file needs to be placed in the Kafka Connect plugins directory on the Kafka Connect worker nodes.

To package your plugin, use Maven or Gradle. For Maven, your pom.xml should include the necessary dependencies and configuration for building the JAR.


<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/POM/4.0.0">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>custom-connect-plugin</artifactId>
    <version>1.0</version>>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>org.apache.kafka</groupId>
            <artifactId>kafka-connect-api</artifactId>
            <version>3.1.0</version>
        </dependency>
    </dependencies>

After packaging, copy the JAR file to the Kafka Connect plugins directory (typically specified by the plugin.path configuration in connect-distributed.properties or connect-standalone.properties).

Configuring and Running Your Custom Plugin

To use your custom connector, create a configuration file and specify the connector class, tasks, and any required configuration properties.


name=custom-source-connector
connector.class=com.example.CustomSourceConnector
tasks.max=1
config.key=some_value
            

Load this configuration file into Kafka Connect using the REST API or by placing it in the Kafka Connect configuration directory. Start or restart Kafka Connect to pick up the new plugin.