Chapter 8. Kafka Connect

Kafka Connect is a tool for streaming data between Apache Kafka and external systems. It provides a framework for moving large amounts of data while maintaining scalability and reliability. Kafka Connect is typically used to integrate Kafka with database, storage, and messaging systems that are external to your Kafka cluster.

Kafka Connect uses connector plug-ins that implement connectivity for different types of external systems. There are two types of connector plug-ins: sink and source. Sink connectors stream data from Kafka to external systems. Source connectors stream data from external systems into Kafka.

Kafka Connect can run in standalone or distributed modes.

Standalone mode
In standalone mode, Kafka Connect runs on a single node with user-defined configuration read from a properties file.
Distributed mode
In distributed mode, Kafka Connect runs across one or more worker nodes and the workloads are distributed among them. You manage connectors and their configuration using an HTTP REST interface.

8.1. Kafka Connect in standalone mode

In standalone mode, Kafka Connect runs as a single process, on a single node. You manage the configuration of standalone mode using properties files.

8.1.1. Configuring Kafka Connect in standalone mode

To configure Kafka Connect in standalone mode, edit the config/connect-standalone.properties configuration file. The following options are the most important.

bootstrap.servers
A list of Kafka broker addresses used as bootstrap connections to Kafka. For example, kafka0.my-domain.com:9092,kafka1.my-domain.com:9092,kafka2.my-domain.com:9092.
key.converter
The class used to convert message keys to and from Kafka format. For example, org.apache.kafka.connect.json.JsonConverter.
value.converter
The class used to convert message payloads to and from Kafka format. For example, org.apache.kafka.connect.json.JsonConverter.
offset.storage.file.filename
Specifies the file in which the offset data is stored.

An example configuration file is provided in the installation directory at config/connect-standalone.properties. For a complete list of all supported Kafka Connect configuration options, see [kafka-connect-configuration-parameters-str].

Connector plug-ins open client connections to the Kafka brokers using the bootstrap address. To configure these connections, use the standard Kafka producer and consumer configuration options prefixed by producer. or consumer..

For more information on configuring Kafka producers and consumers, see Appendix D, Producer configuration parameters and Appendix C, Consumer configuration parameters.

8.1.2. Configuring connectors in Kafka Connect in standalone mode

You can configure connector plug-ins for Kafka Connect in standalone mode using properties files. Most configuration options are specific to each connector. The following options apply to all connectors:

name
The name of the connector, which must be unique within the current Kafka Connect instance.
connector.class
The class of the connector plug-in. For example, org.apache.kafka.connect.file.FileStreamSinkConnector.
tasks.max
The maximum number of tasks that the specified connector can use. Tasks enable the connector to perform work in parallel. The connector might create fewer tasks than specified.
key.converter
The class used to convert message keys to and from Kafka format. This overrides the default value set by the Kafka Connect configuration. For example, org.apache.kafka.connect.json.JsonConverter.
value.converter
The class used to convert message payloads to and from Kafka format. This overrides the default value set by the Kafka Connect configuration. For example, org.apache.kafka.connect.json.JsonConverter.

Additionally, you must set at least one of the following options for sink connectors:

topics
A comma-separated list of topics used as input.
topics.regex
A Java regular expression of topics used as input.

For all other options, see the documentation for the available connectors.

AMQ Streams includes example connector configuration files – see config/connect-file-sink.properties and config/connect-file-source.properties in the AMQ Streams installation directory.

8.1.3. Running Kafka Connect in standalone mode

This procedure describes how to configure and run Kafka Connect in standalone mode.

Prerequisites

  • An installed and running AMQ Streams} cluster.

Procedure

  1. Edit the /opt/kafka/config/connect-standalone.properties Kafka Connect configuration file and set bootstrap.server to point to your Kafka brokers. For example:

    bootstrap.servers=kafka0.my-domain.com:9092,kafka1.my-domain.com:9092,kafka2.my-domain.com:9092
  2. Start Kafka Connect with the configuration file and specify one or more connector configurations.

    su - kafka
    /opt/kafka/bin/connect-standalone.sh /opt/kafka/config/connect-standalone.properties connector1.properties
    [connector2.properties ...]
  3. Verify that Kafka Connect is running.

       jcmd | grep ConnectStandalone

Additional resources

8.2. Kafka Connect in distributed mode

In distributed mode, Kafka Connect runs across one or more worker nodes and the workloads are distributed among them. You manage connector plug-ins and their configuration using the HTTP REST interface.

8.2.1. Configuring Kafka Connect in distributed mode

To configure Kafka Connect in distributed mode, edit the config/connect-distributed.properties configuration file. The following options are the most important.

bootstrap.servers
A list of Kafka broker addresses used as bootstrap connections to Kafka. For example, kafka0.my-domain.com:9092,kafka1.my-domain.com:9092,kafka2.my-domain.com:9092.
key.converter
The class used to convert message keys to and from Kafka format. For example, org.apache.kafka.connect.json.JsonConverter.
value.converter
The class used to convert message payloads to and from Kafka format. For example, org.apache.kafka.connect.json.JsonConverter.
group.id
The name of the distributed Kafka Connect cluster. This must be unique and must not conflict with another consumer group ID. The default value is connect-cluster.
config.storage.topic
The Kafka topic used to store connector configurations. The default value is connect-configs.
offset.storage.topic
The Kafka topic used to store offsets. The default value is connect-offset.
status.storage.topic
The Kafka topic used for worker node statuses. The default value is connect-status.

AMQ Streams includes an example configuration file for Kafka Connect in distributed mode – see config/connect-distributed.properties in the AMQ Streams installation directory.

For a complete list of all supported Kafka Connect configuration options, see Appendix F, Kafka Connect configuration parameters.

Connector plug-ins open client connections to the Kafka brokers using the bootstrap address. To configure these connections, use the standard Kafka producer and consumer configuration options prefixed by producer. or consumer..

For more information on configuring Kafka producers and consumers, see Appendix D, Producer configuration parameters and Appendix C, Consumer configuration parameters.

8.2.2. Configuring connectors in distributed Kafka Connect

HTTP REST Interface

Connectors for distributed Kafka Connect are configured using HTTP REST interface. The REST interface listens on port 8083 by default. It supports following endpoints:

GET /connectors
Return a list of existing connectors.
POST /connectors
Create a connector. The request body has to be a JSON object with the connector configuration.
GET /connectors/<name>
Get information about a specific connector.
GET /connectors/<name>/config
Get configuration of a specific connector.
PUT /connectors/<name>/config
Update the configuration of a specific connector.
GET /connectors/<name>/status
Get the status of a specific connector.
PUT /connectors/<name>/pause
Pause the connector and all its tasks. The connector will stop processing any messages.
PUT /connectors/<name>/resume
Resume a paused connector.
POST /connectors/<name>/restart
Restart a connector in case it has failed.
DELETE /connectors/<name>
Delete a connector.
GET /connector-plugins
Get a list of all supported connector plugins.

Connector configuration

Most configuration options are connector specific and included in the documentation for the connectors. The following fields are common for all connectors.

name
Name of the connector. Must be unique within a given Kafka Connect instance.
connector.class
Class of the connector plugin. For example org.apache.kafka.connect.file.FileStreamSinkConnector.
tasks.max
The maximum number of tasks used by this connector. Tasks are used by the connector to parallelise its work. Connetors may create fewer tasks than specified.
key.converter
Class used to convert message keys to and from Kafka format. This overrides the default value set by the Kafka Connect configuration. For example, org.apache.kafka.connect.json.JsonConverter.
value.converter
Class used to convert message payloads to and from Kafka format. This overrides the default value set by the Kafka Connect configuration. For example, org.apache.kafka.connect.json.JsonConverter.

Additionally, one of the following options must be set for sink connectors:

topics
A comma-separated list of topics used as input.
topics.regex
A Java regular expression of topics used as input.

For all other options, see the documentation for the specific connector.

AMQ Streams includes example connector configuration files. They can be found in config/connect-file-sink.properties and config/connect-file-source.properties in the AMQ Streams installation directory.

8.2.3. Running distributed Kafka Connect

This procedure describes how to configure and run Kafka Connect in distributed mode.

Prerequisites

  • An installed and running AMQ Streams cluster.

Running the cluster

  1. Edit the /opt/kafka/config/connect-distributed.properties Kafka Connect configuration file on all Kafka Connect worker nodes.

    • Set the bootstrap.server option to point to your Kafka brokers.
    • Set the group.id option.
    • Set the config.storage.topic option.
    • Set the offset.storage.topic option.
    • Set the status.storage.topic option.

      For example:

      bootstrap.servers=kafka0.my-domain.com:9092,kafka1.my-domain.com:9092,kafka2.my-domain.com:9092
      group.id=my-group-id
      config.storage.topic=my-group-id-configs
      offset.storage.topic=my-group-id-offsets
      status.storage.topic=my-group-id-status
  2. Start the Kafka Connect workers with the /opt/kafka/config/connect-distributed.properties configuration file on all Kafka Connect nodes.

    su - kafka
    /opt/kafka/bin/connect-distributed.sh /opt/kafka/config/connect-distributed.properties
  3. Verify that Kafka Connect is running.

    jcmd | grep ConnectDistributed

Additional resources

8.2.4. Creating connectors

This procedure describes how to use the Kafka Connect REST API to create a connector plug-in for use with Kafka Connect in distributed mode.

Prerequisites

  • A Kafka Connect installation running in distributed mode.

Procedure

  1. Prepare a JSON payload with the connector configuration. For example:

    {
      "name": "my-connector",
      "config": {
      "connector.class": "org.apache.kafka.connect.file.FileStreamSinkConnector",
        "tasks.max": "1",
        "topics": "my-topic-1,my-topic-2",
        "file": "/tmp/output-file.txt"
      }
    }
  2. Send a POST request to <KafkaConnectAddress>:8083/connectors to create the connector. The following example uses curl:

    curl -X POST -H "Content-Type: application/json" --data @sink-connector.json http://connect0.my-domain.com:8083/connectors
  3. Verify that the connector was deployed by sending a GET request to <KafkaConnectAddress>:8083/connectors. The following example uses curl:

    curl http://connect0.my-domain.com:8083/connectors

8.2.5. Deleting connectors

This procedure describes how to use the Kafka Connect REST API to delete a connector plug-in from Kafka Connect in distributed mode.

Prerequisites

  • A Kafka Connect installation running in distributed mode.

Deleting connectors

  1. Verify that the connector exists by sending a GET request to <KafkaConnectAddress>:8083/connectors/<ConnectorName>. The following example uses curl:

    curl http://connect0.my-domain.com:8083/connectors
  2. To delete the connector, send a DELETE request to <KafkaConnectAddress>:8083/connectors. The following example uses curl:

    curl -X DELETE http://connect0.my-domain.com:8083/connectors/my-connector
  3. Verify that the connector was deleted by sending a GET request to <KafkaConnectAddress>:8083/connectors. The following example uses curl:

    curl http://connect0.my-domain.com:8083/connectors

8.3. Connector plug-ins

The following connector plug-ins are included with AMQ Streams.

FileStreamSink Reads data from Kafka topics and writes the data to a file.

FileStreamSource Reads data from a file and sends the data to Kafka topics.

You can add more connector plug-ins if needed. Kafka Connect searches for and runs additional connector plug-ins at startup. To define the path that kafka Connect searches for plug-ins, set the plugin.path configuration option:

plugin.path=/opt/kafka/connector-plugins,/opt/connectors

The plugin.path configuration option can contain a comma-separated list of paths.

When running Kafka Connect in distributed mode, plug-ins must be made available on all worker nodes.

8.4. Adding connector plugins

This procedure shows you how to add additional connector plug-ins.

Prerequisites

  • An installed and running AMQ Streams cluster.

Procedure

  1. Create the /opt/kafka/connector-plugins directory.

    su - kafka
    mkdir /opt/kafka/connector-plugins
  2. Edit the /opt/kafka/config/connect-standalone.properties or /opt/kafka/config/connect-distributed.properties Kafka Connect configuration file, and set the plugin.path option to /opt/kafka/connector-plugins. For example:

    plugin.path=/opt/kafka/connector-plugins
  3. Copy your connector plug-ins to /opt/kafka/connector-plugins.
  4. Start or restart the Kafka Connect workers.

Additional resources