Kafka

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Kafka is an open-source distributed event streaming platform, organized in the form of a log with message publishers and subscribers. The Kafka dlt verified source loads data using the Confluent Kafka API to the destination of your choice. See a pipeline example.

The resource that can be loaded:

Name	Description
kafka_consumer	Extracts messages from Kafka topics

Setup guide

Grab Kafka cluster credentials

1. Follow the Kafka Setup to tweak a project.
2. Follow the Configuration to get the project credentials.

Initialize the verified source

To get started with your data pipeline, follow these steps:

1. Enter the following command:

   dlt init kafka duckdb

   This command will initialize the pipeline example with Kafka as the source and duckdb as the destination.

2. If you'd like to use a different destination, simply replace duckdb with the name of your preferred destination.

3. After running this command, a new directory will be created with the necessary files and configuration settings to get started.

For more information, read the Walkthrough: Add a verified source.

Add credentials

1. In the .dlt folder, there's a file called secrets.toml. It's where you store sensitive information securely, like access tokens. Keep this file safe.

   Use the following format for service account authentication:

[sources.kafka.credentials]
bootstrap_servers="web.address.gcp.confluent.cloud:9092"
group_id="test_group"
security_protocol="SASL_SSL"
sasl_mechanisms="PLAIN"
sasl_username="example_username"
sasl_password="example_secret"

2. Enter credentials for your chosen destination as per the docs.

Run the pipeline

1. Before running the pipeline, ensure that you have installed all the necessary dependencies by running the command:

   pip install -r requirements.txt

2. You're now ready to run the pipeline! To get started, run the following command:

   python kafka_pipeline.py

3. Once the pipeline has finished running, you can verify that everything loaded correctly by using the following command:

   dlt pipeline <pipeline_name> show

For more information, read the Walkthrough: Run a pipeline.

If you created a topic and start reading from it immediately, the brokers may not yet be synchronized, and the offset from which dlt reads messages may become invalid. In this case, the resource will return no messages. Pending messages will be received on the next run (or when brokers synchronize).

Sources and resources

dlt works on the principle of sources and resources.

Source kafka_consumer

This function retrieves messages from the given Kafka topics.

@dlt.resource(name="kafka_messages", table_name=lambda msg: msg["_kafka"]["topic"], standalone=True)
def kafka_consumer(
    topics: Union[str, List[str]],
    credentials: Union[KafkaCredentials, Consumer] = dlt.secrets.value,
    msg_processor: Optional[Callable[[Message], Dict[str, Any]]] = default_msg_processor,
    batch_size: Optional[int] = 3000,
    batch_timeout: Optional[int] = 3,
    start_from: Optional[TAnyDateTime] = None,
) -> Iterable[TDataItem]:
   ...

topics: A list of Kafka topics to be extracted.

credentials: By default, it is initialized with the data from the secrets.toml. It may be used explicitly to pass an initialized Kafka Consumer object.

msg_processor: A function that will be used to process every message read from the given topics before saving them in the destination. It can be used explicitly to pass a custom processor. See the default processor as an example of how to implement processors.

batch_size: The number of messages to extract from the cluster at once. It can be set to tweak performance.

batch_timeout: The maximum timeout (in seconds) for a single batch reading operation. It can be set to tweak performance.

start_from: A timestamp, starting from which the messages must be read. When passed, dlt asks the Kafka cluster for an offset, which is actual for the given timestamp, and starts to read messages from this offset.

Customization

Create your own pipeline

1. Configure the pipeline by specifying the pipeline name, destination, and dataset as follows:

   pipeline = dlt.pipeline(
        pipeline_name="kafka",     # Use a custom name if desired
        destination="duckdb",      # Choose the appropriate destination (e.g., duckdb, redshift, post)
        dataset_name="kafka_data"  # Use a custom name if desired
   )

2. To extract several topics:

   topics = ["topic1", "topic2", "topic3"]
   
   source = kafka_consumer(topics)
   pipeline.run(source, write_disposition="replace")

3. To extract messages and process them in a custom way:

    def custom_msg_processor(msg: confluent_kafka.Message) -> Dict[str, Any]:
        return {
            "_kafka": {
                "topic": msg.topic(),  # required field
                "key": msg.key().decode("utf-8"),
                "partition": msg.partition(),
            },
            "data": msg.value().decode("utf-8"),
        }
   
    data = kafka_consumer("topic", msg_processor=custom_msg_processor)
    pipeline.run(data)

4. To extract messages, starting from a timestamp:

    data = kafka_consumer("topic", start_from=pendulum.datetime(2023, 12, 15))
    pipeline.run(data)