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Google Cloud Pub/Sub Group Kafka Connector

The Google Cloud Pub/Sub Group Kafka Connector library provides Google Cloud Platform (GCP) first-party connectors for Pub/Sub products with Kafka Connect. You can use the library to transmit data from Apache Kafka to Cloud Pub/Sub or Pub/Sub Lite and vice versa.

• CloudPubSubSinkConnector is a sink connector that reads records from Kafka and publishes them to Cloud Pub/Sub.
• CloudPubSubSourceConnector is a source connector that reads messages from Cloud Pub/Sub and writes them to Kafka.
• PubSubLiteSinkConnector is a sink connector that reads records from Kafka and publishes them to Pub/Sub Lite.
• PubSubLiteSourceConnector is a source connector that reads messages from Pub/Sub Lite and writes them to Kafka.

Prerequisites

You must have a GCP project in order to use Cloud Pub/Sub or Pub/Sub Lite.

Follow these setup steps for Pub/Sub before doing the quickstart.

Follow these setup steps for Pub/Sub Lite before doing the quickstart.

For general information on how to authenticate with GCP when using the Google Cloud Pub/Sub Group Kafka Connector library, please visit Provide credentials for Application Default Credentials.

Quickstart

In this quickstart, you will learn how to send data from a Kafka topic to a Pub/Sub or Pub/Sub Lite topic and vice versa, using Kafka Connect running locally in standalone mode (single process).

1. Follow the Kafka quickstart to download Kafka, start the Kafka environment, and create a Kafka topic.

   Note: Please use the same Kafka API major version as that used by the connector. Otherwise, the connector may not work properly. Check the Kafka version used by the connector in pom.xml.

2. Acquire the connector jar.

3. Update your Kafka Connect configurations.

   Open /config/connect-standalone.properties in the Kafka download folder. Add the filepath of the downloaded connector jar to plugin.path and uncomment the line if needed. In addition, because the connector is using Kafka Connect in standalone mode, include offset.storage.file.filename with a valid filename to store offset data in.

4. Create a pair of Pub/Sub or Pub/Sub Lite topic and subscription.

   • CloudPubSubSinkConnector and CloudPubSubSourceConnector
     • Create a pair of Pub/Sub topic and subscription
   • PubSubLiteSinkConnector and PubSubLiteSourceConnector
     • Create a pair of Pub/Sub Lite topic and subscription.

5. Update the connector configurations.

   Open the connector configuration files at /config. Update variables labeled TODO (developer) with appropriate input.

   • CloudPubSubSinkConnector

     1. Open cps-sink-connector.properties.
     2. Update topics, cps.project, and cps.topic.

   • CloudPubSubSourceConnector

     1. Open cps-source-connector.properties.
     2. Update kafka.topic, cps.project, and cps.subscription.

   • PubSubLiteSinkConnector

     1. Open pubsub-lite-sink-connector.properties.
     2. Update topics, pubsublite.project, pubsublite.location and pubsublite.topic.

   • PubSubLiteSourceConnector

     1. Open pubsub-lite-source-connector.properties.
     2. Update kafka.topic, pubsublite.project, pubsublite.location and pubsublite.subscription.

6. Run the following command to start the appropriate sink or source connector. You can run multiple connector tasks at the same time.

   > bin/connect-standalone.sh \
     config/connect-standalone.properties \
     path/to/pubsub/sink/connector.properties [source.connector.properties ...]
   

7. Test the connector.

   • CloudPubSubSinkConnector

     1. Follow the instructions in the Kafka quickstart to publish a message to the Kafka topic.
     2. Pull the message from your Pub/Sub subscription.

   • CloudPubSubSourceConnector

     1. Publish a message to your Pub/Sub topic.
     2. Follow the instructions in the Kafka quickstart to read the message from your Kafka topic.

   • PubSubLiteSinkConnector

     1. Publish a message to your Pub/Sub Lite topic.
     2. Follow the instructions in the Kafka quickstart to read the message from your Kafka topic.

   • PubSubLiteSourceConnector

     1. Follow the instructions in the Kafka quickstart to publish a message to the Kafka topic.
     2. Pull the message from your Pub/Sub Lite subscription.

Acquire the connector

The connector is available from Maven Central repository. Select the latest version of the connector, then download "jar" from the Downloads dropdown menu.

You can also build the connector from head.

Run the connector

Please refer to Kafka User Guide for general information on running connectors using Kafka Connect.

To run this connector using Kafka Connect in standalone mode, follow these steps:

1. Copy the connector jar where you will run Kafka Connect.

2. Create a configuration file for your Kafka Connect instance. Make sure to include the filepath to the connector jar in plugin.path.

3. Make a copy of the connector configuration files at /config and update the configuration options accordingly.

4. Start Kafka Connect with your connector with the following command:

   > bin/connect-standalone.sh config/connect-standalone.properties connector1.properties [connector2.properties ...]
   

5. If running the Kafka Connect behind a proxy, export the KAFKA_OPTS variable with options for connecting around the proxy.

   > export KAFKA_OPTS="-Dhttp.proxyHost=<host> -Dhttp.proxyPort=<port> -Dhttps.proxyHost=<host> -Dhttps.proxyPort=<port>"
   

When running the connector on a Kafka cluster in distributed mode, "the connector configurations are not passed on the command line. Instead, use the REST API described below to create, modify, and destroy connectors" (Kafka User Guide).

Pub/Sub connector configs

In addition to the Kafka Connect configurations supplied by the Kafka Connect API, the Pub/Sub connector supports the following configurations:

Source Connector

Sink Connector

Pub/Sub Lite connector configs

In addition to the Kafka Connect configurations supplied by the Kafka Connect API, the Pub/Sub Lite connector supports the following configurations:

Source Connector

Sink Connector

Shared miscellaneous configs

These following configurations are shared by the Pub/Sub and Pub/Sub Lite connectors.

Schema support and data model

Pub/Sub Connector

The message data field of PubSubMessage is a ByteString object that translates well to and from the byte[] bodies of Kafka messages. We recommend using a converter that produces primitive data types (i.e. integer, float, string, or bytes types) where possible to avoid deserializing and re-serializing the same message body.

Additionally, a Pub/Sub message cannot exceed 10 MB. We recommend checking your message.max.bytes configuration to prevent possible errors.

The sink connector handles message conversion in the following way:

• Integer, float, string, and bytes types in Kafka messages are passed directly into the Pub/Sub message body as bytes.
• Map and struct types in Kafka messages are stored as Pub/Sub attributes. Pub/Sub attributes only supports string to string mapping. To make the connector as versatile as possible, the toString() method is called on objects passed in as the key or value for a map and the value for a struct.
  • If you set the messageBodyName configuration to a struct field or map key, the value of the structure field or the map value (of integer, byte, float, and array type) will be stored in the Pub/Sub message body as bytes.
• Only primitive array types are supported due to potential collisions of field names or keys of a struct/map array. The connector handles arrays in a fairly predictable fashion, where values are concatenated into a ByteString object.
• The record-level key for a Kafka message is stored in Pub/Sub message attributes as a string, with the name "key".

Note: Pub/Sub message attributes have the following limitations:

• Attributes per message: 100
• Attribute key size: 256 bytes
• Attribute value size: 1024 bytes

The connector will transform Kafka record-level message headers that meet these limitations and ignore those that don't.

The source connector handles the conversion from a Pub/Sub message into a Kafka SourceRecord in a similar way:

• The source connector searches for kafka.key.attribute in the attributes of a Pub/Sub message. If found, it will be used as the Kafka message key as a string. Otherwise, the Kafka message key will be set to null.
• If a Pub/Sub message has no attributes, the message body will be stored as a byte[] object for the Kafka message value.
• If a Pub/Sub message contains attributes other than kafka.key.attribute, they will be assigned a struct schema. The message attribute keys will become struct field names, and the corresponding attribute values will become values of those struct fields. The message body will be transformed into a struct field of name message and of type bytes.
  • To carry forward the structure of data stored in Pub/Sub message attributes, we recommend using a converter that represents a struct schema type, like JsonConverter.

Pub/Sub Lite Connector

Pub/Sub Lite messages have the following structure:

class Message {

  ByteString key;
  ByteString data;
  ListMultimap<String, ByteString> attributes;
  Optional<Timestamp> eventTime;
}

This table shows how each field in a Kafka SinkRecord maps to a Pub/Sub Lite message by the sink connector:

When a key, value or header value with a schema is encoded as a ByteString, the following logic will be used:

• Null schemas are treated as Schema.STRING_SCHEMA
• Top-level BYTES payloads are unmodified
• Top-level STRING payloads are encoded using copyFromUtf8
• Top-level Integral payloads are converted using copyFromUtf8(Long.toString( x.longValue()))
• Top-level Floating point payloads are converted using copyFromUtf8( Double.toString(x.doubleValue()))
• All other payloads are encoded into a protobuf Value, then converted to a ByteString
  • Nested STRING fields are encoded into a protobuf Value
  • Nested BYTES fields are encoded to a protobuf Value holding the base64 encoded bytes
  • Nested Numeric fields are encoded as a double into a protobuf Value
  • Maps with Array, Map, or Struct keys are not supported
    • BYTES keys in maps are base64 encoded
    • Integral keys are converted using Long.toString(x.longValue())
    • Floating point keys are converted using Double.toString( x.doubleValue())

The source connector performs a one-to-one mapping from SequencedMessage fields to their Kafka SourceRecord counterparts.

Pub/Sub Lite message of empty message.key fields will have their field values be converted to null, and they will be assigned to Kafka partitions using the round-robin scheme. Messages with identical, non-empty keys will be routed to the same Kafka partition.

Build the connector

These instructions assume you are using Maven.

1. Clone this repository:

   > git clone https://github.com/googleapis/java-pubsub-group-kafka-connector
   

2. Package the connector jar:

   > mvn clean package -DskipTests=True
   

   You should see the resulting jar at target/pubsub-group-kafka-connector-${VERSION}-SNAPSHOT.jar on success.

Versioning

This library follows Semantic Versioning.

Contributing

Contributions to this library are always welcome and highly encouraged.

See CONTRIBUTING for more information how to get started.

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms. See Code of Conduct for more information.

License

Apache 2.0 - See LICENSE for more information.