GCP Pub/Sub

The Kafka connector is designed to seamlessly ingest records from GCP Pub/Sub topics and queues into your Kafka cluster. This makes it useful for backing up or streaming data from Pub/Sub to your Kafka infrastructure. This connector provides robust support for at least once semantics (this connector ensures that each record reaches the Kafka topic at least once).

Configuration Example 

connect.pubsub.kcql=insert into `kafka_topic_to_write_to` select * from `gcp-subscription-id`


NameDescriptionTypeAvailable ValuesDefault Value
connect.pubsub.gcp.auth.modeSpecifies the authentication mode for connecting to GCP.string“Credentials”, “File” or “Default”“Default”
connect.pubsub.gcp.credentialsFor “auth.mode” credentials: GCP Authentication credentials string.string(Empty)
connect.pubsub.gcp.fileFor “auth.mode” file: Local file path for file containing GCP authentication credentials.string(Empty)
connect.pubsub.gcp.project.idGCP Project ID.string(Empty)
connect.pubsub.kcqlKafka Connect Query Language (KCQL) Configuration to control the connector behaviourstringkcql configuration
connect.pubsub.output.modeOutput mode. Please see Output Modes documentation below.“Default” or “Compatibility”“Default”

KCQL (Kafka Connect Query Language) 

The connector uses a SQL-like syntax to configure the connector behaviour. The full KCQL syntax is:

    INSERT INTO kafka-topic
    SELECT *
    FROM subscriptionId

Please note that you can employ escaping within KCQL for the INSERT INTO and SELECT * FROM clauses when necessary. For example, if you need to use a topic name that contains a hyphen, you can escape it as follows:

    INSERT INTO `my-topic-with-hyphen`
    SELECT *
    FROM bucketAddress:pathPrefix

Source Subscription ID and Target Topic 

The source and target of the data are specified via the INSERT INTO... SELECT * FROM clause. The connector will write all the records to the given topic, from the given subscription:

INSERT INTO my-topic SELECT * FROM subscriptionId;

KCQL Properties 

The PROPERTIES clause is optional and adds a layer of configurability to the connector. It enhances versatility by permitting the application of multiple configurations (delimited by ‘,’).

The following properties are supported:

NameDescriptionTypeDefault Value
batch.sizeThe maximum number of messages the connector will retrieve and process at one time per polling request (per KCQL mapping).int1000
cache.ttlThe maximum amount of time (in milliseconds) to store message data to allow acknowledgement of a message.long1 hour
queue.maxData is loaded into a queue asynchronously so that it stands ready when the poll call is activated. Control the maximum number of records to hold in the queue per KCQL mapping.int10000

Auth Mode 

The connector offers two distinct authentication modes:

  • Default: This mode relies on the default GCP authentication chain, simplifying the authentication process.
  • File: This mode uses a local (to the connect worker) path for a file containing GCP authentication credentials.
  • Credentials: In this mode, explicit configuration of a GCP Credentials string is required for authentication.

The simplest example to configure in the connector is the “Default” mode, as this requires no other configuration.


When selecting the “Credentials” mode, it is essential to provide the necessary credentials. Alternatively, if you prefer not to configure these properties explicitly, the connector will follow the credentials retrieval order as described here.

Here’s an example configuration for the “Credentials” mode:


And here is an example configuration using the “File” mode:


Remember when using file mode the file will need to exist on every worker node in your Kafka connect cluster and be readable by the Kafka Connect process.

For enhanced security and flexibility when using either the “Credentials” mode, it is highly advisable to utilize Connect Secret Providers. You can find detailed information on how to use the Connect Secret Providers here. This approach ensures robust security practices while handling access credentials.

Output Modes 

Two modes are available: Default Mode and Compatibility Mode.

Compatibility Mode is intended to ensure compatibility with existing tools, while Default Mode offers a simpler modern redesign of the functionality.

You can choose whichever suits your requirements.

Default Mode 



Record Schema 

Each Pub/Sub message is transformed into a single Kafka record, structured as follows:

  • Kafka Key: A String of the Pub/Sub MessageID.
  • Kafka Value: The Pub/Sub message value as BYTES.
  • Kafka Headers: Includes the “PublishTimestamp” (in seconds) and all Pub/Sub message attributes mapped as separate headers.

Key Schema 

The Kafka Key is mapped from the Pub/Sub MessageID, a unique ID for a Pub/Sub message.

Value Schema 

The Kafka Value is mapped from the body of the Pub/Sub message.

Headers Schema 

The Kafka Headers include:

  • PublishTimestamp: Long value representing the time when the Pub/Sub message was published, in seconds.
  • GCPProjectID: The GCP Project
  • PubSubTopicID: The Pub/Sub Topic ID.
  • PubSubSubscriptionID: The Pub/Sub Subscription ID.
  • All Pub/Sub message attributes: Each attribute from the Pub/Sub message is mapped as a separate header.

Compatibility Mode 



Record Schema 

Each Pub/Sub message is transformed into a single Kafka record, structured as follows:

  • Kafka Key: Comprises the project ID, message ID, and subscription ID of the Pub/Sub message.
  • Kafka Value: Contains the message data and attributes from the Pub/Sub message.

Key Schema 

The Key is a structure with these fields:

Field NameSchema TypeDescription
ProjectIdStringThe Pub/Sub project containing the topic from which messages are polled.
TopicIdStringThe Pub/Sub topic containing the messages.
SubscriptionIdStringThe Pub/Sub subscription of the Pub/Sub topic.
MessageIdStringA unique ID for a Pub/Sub message.

Value Schema 

The Value is a structure with these fields:

Field NameSchema TypeDescription
MessageDataOptional StringThe body of the Pub/Sub message.
AttributeMapOptional StringThe attribute map associated with the Pub/Sub message.
Last modified: July 17, 2024