Create a stream reactor source connector from Apache Cassandra® to Apache Kafka®

The Apache Cassandra® stream reactor source connector enables you to move data from a Apache Cassandra® database to an Aiven for Apache Kafka® cluster. The Lenses.io implementation enables you to write KCQL transformations on the topic data before sending it to the Apache Kafka cluster.

note

You can check the full set of available parameters and configuration options in the connector's documentation.

Prerequisites

To setup a Apache Cassandra source connector, you need an Aiven for Apache Kafka service with Kafka Connect enabled or a dedicated Aiven for Apache Kafka Connect cluster.

Furthermore you need to collect the following information about the target Cassandra database upfront:

CASSANDRA_HOSTNAME: The Cassandra hostname
CASSANDRA_PORT: The Cassandra port
CASSANDRA_USERNAME: The Cassandra username
CASSANDRA_PASSWORD: The Cassandra password
CASSANDRA_SSL: The Cassandra SSL setting, can be true, false or default
CASSANDRA_KEYSTORE: The path to the Keystore containing the CA certificate, used when connection is secured via SSL
CASSANDRA_KEYSTORE_PASSWORD: The Keystore password, used when connection is secured via SSL

note

If you're using Aiven for Apache Cassandra, you can use the following keystore values

CASSANDRA_TRUSTSTORE: /run/aiven/keys/public.truststore.jks
CASSANDRA_TRUSTSTORE_PASSWORD: password

CASSANDRA_KEYSPACE: The Cassandra keyspace to use to source the data from
KCQL_TRANSFORMATION: The KCQL syntax to parse the topic data, should be in the format:
```
INSERT INTO APACHE_KAFKA_TOPIC
SELECT LIST_OF_FIELDS
FROM CASSANDRA_TABLE
[PK CASSANDRA_TABLE_COLUMN]
[INCREMENTAL_MODE=MODE]
```
warning
By default the connector acts in bulk mode, extracting all the rows from the Cassandra table on a polling interval and pushing them to the Apache Kafka topic. You can however define incremental options by defining the incremental mode and primary key.
APACHE_KAFKA_HOST: The hostname of the Apache Kafka service, only needed when using Avro as data format
SCHEMA_REGISTRY_PORT: The Apache Kafka's schema registry port, only needed when using Avro as data format
SCHEMA_REGISTRY_USER: The Apache Kafka's schema registry username, only needed when using Avro as data format
SCHEMA_REGISTRY_PASSWORD: The Apache Kafka's schema registry user password, only needed when using Avro as data format

note

If you're using Aiven for Cassandra and Aiven for Apache Kafka, the above details are available in the Aiven console service Overview tab or via the dedicated avn service get command with the Aiven CLI.

The SCHEMA_REGISTRY related parameters are available in the Aiven for Apache Kafka® service page, Overview tab, and Schema Registry subtab

As of version 3.0, Aiven for Apache Kafka no longer supports Confluent Schema Registry. For more information, read the article describing the replacement, Karapace

Setup an Apache Cassandra source connector with Aiven Console

The following example demonstrates how to setup an Apache Cassandra source connector for Apache Kafka using the Aiven Console.

Define a Kafka Connect configuration file

Define the connector configurations in a file (we'll refer to it with the name cassandra_source.json) with the following content, creating a file is not strictly necessary but allows to have all the information in one place before copy/pasting them in the Aiven Console:

{
    "name":"CONNECTOR_NAME",
    "connector.class": "com.datamountaineer.streamreactor.connect.cassandra.source.CassandraSourceConnector",
    "connect.cassandra.host": "CASSANDRA_HOSTNAME",
    "connect.cassandra.port": "CASSANDRA_PORT",
    "connect.cassandra.username": "CASSANDRA_USERNAME",
    "connect.cassandra.password": "CASSANDRA_PASSWORD",
    "connect.cassandra.ssl.enabled": "CASSANDRA_SSL",
    "connect.cassandra.trust.store.path": "CASSANDRA_TRUSTSTORE",
    "connect.cassandra.trust.store.password": "CASSANDRA_TRUSTSTORE_PASSWORD",
    "connect.cassandra.key.space": "CASSANDRA_KEYSPACE",
    "connect.cassandra.kcql": "KCQL_TRANSFORMATION",
    "key.converter": "io.confluent.connect.avro.AvroConverter",
    "key.converter.schema.registry.url": "https://APACHE_KAFKA_HOST:SCHEMA_REGISTRY_PORT",
    "key.converter.basic.auth.credentials.source": "USER_INFO",
    "key.converter.schema.registry.basic.auth.user.info": "SCHEMA_REGISTRY_USER:SCHEMA_REGISTRY_PASSWORD",
    "value.converter": "io.confluent.connect.avro.AvroConverter",
    "value.converter.schema.registry.url": "https://APACHE_KAFKA_HOST:SCHEMA_REGISTRY_PORT",
    "value.converter.basic.auth.credentials.source": "USER_INFO",
    "value.converter.schema.registry.basic.auth.user.info": "SCHEMA_REGISTRY_USER:SCHEMA_REGISTRY_PASSWORD"
}

The configuration file contains the following entries:

name: the connector name, replace CONNECTOR_NAME with the name you want to use for the connector.
connect.cassandra.*: source parameters collected in the prerequisite phase.
key.converter and value.converter: defines the messages data format in the Apache Kafka topic. The io.confluent.connect.avro.AvroConverter converter translates messages from the Avro format. To retrieve the messages schema we use Aiven's Karapace schema registry as specified by the schema.registry.url parameter and related credentials.

note

The key.converter and value.converter sections define how the topic messages will be parsed and needs to be included in the connector configuration.

When using Avro as source data format, you need to set following parameters

value.converter.schema.registry.url: pointing to the Aiven for Apache Kafka schema registry URL in the form of https://APACHE_KAFKA_HOST:SCHEMA_REGISTRY_PORT with the APACHE_KAFKA_HOST and SCHEMA_REGISTRY_PORT parameters retrieved in the previous step.
value.converter.basic.auth.credentials.source: to the value USER_INFO, since you're going to login to the schema registry using username and password.
value.converter.schema.registry.basic.auth.user.info: passing the required schema registry credentials in the form of SCHEMA_REGISTRY_USER:SCHEMA_REGISTRY_PASSWORD with the SCHEMA_REGISTRY_USER and SCHEMA_REGISTRY_PASSWORD parameters retrieved in the previous step.

Create a Kafka Connect connector with the Aiven Console

To create a Kafka Connect connector, follow these steps:

Log in to the Aiven Console and select the Aiven for Apache Kafka® or Aiven for Apache Kafka Connect® service where the connector needs to be defined.
Select Connectors from the left sidebar.
Select Create New Connector, the button is enabled only for services with Kafka Connect enabled.
Select Stream Reactor Cassandra Source.
In the Common tab, locate the Connector configuration text box and select on Edit.
Paste the connector configuration (stored in the cassandra_source.json file) in the form.
Select Apply.

note
The Aiven Console parses the configuration file and fills the relevant UI fields. You can review the UI fields across the various tab and change them if necessary. The changes will be reflected in JSON format in the Connector configuration text box.
After all the settings are correctly configured, select Create new connector.
Verify the connector status under the Connectors screen.
Verify the presence of the data in the target Cassandra service.

You can also create connectors using the Aiven CLI command.

Example: Create a Cassandra source connector

If you have a Cassandra table named students in the students_keyspace keyspace, with four columns (id, name, age and timestamp_added) and you want to load incrementally an Apache Kafka topic called students_topic, you can use the following connector configuration, after replacing the placeholders for CASSANDRA_HOST, CASSANDRA_PORT, CASSANDRA_USERNAME, CASSANDRA_PASSWORD, CASSANDRA_KEYSTORE, CASSANDRA_KEYSTORE_PASSWORD, CASSANDRA_TRUSTSTORE, CASSANDRA_TRUSTSTORE_PASSWORD, CASSANDRA_KEYSPACE:

{
    "name": "my-cassandra-source",
    "connector.class": "com.datamountaineer.streamreactor.connect.cassandra.source.CassandraSinkConnector",
    "topics": "TOPIC_LIST",
    "connect.cassandra.host": "CASSANDRA_HOSTNAME",
    "connect.cassandra.port": "CASSANDRA_PORT",
    "connect.cassandra.username": "CASSANDRA_USERNAME",
    "connect.cassandra.password": "CASSANDRA_PASSWORD",
    "connect.cassandra.ssl.enabled": "CASSANDRA_SSL",
    "connect.cassandra.trust.store.path": "CASSANDRA_TRUSTSTORE",
    "connect.cassandra.trust.store.password": "CASSANDRA_TRUSTSTORE_PASSWORD",
    "connect.cassandra.key.space": "students_keyspace",
    "value.converter": "org.apache.kafka.connect.json.JsonConverter",
    "connect.cassandra.kcql": "INSERT INTO students_topic SELECT id, name, age, timestamp_added FROM students PK timestamp_added INCREMENTALMODE=TIMESTAMP"
}

The configuration file contains the following peculiarities:

"topics": "students": setting the topic to source
"connect.cassandra": the connection parameters placeholders
"value.converter": "org.apache.kafka.connect.json.JsonConverter": the topic will be populated in JSON format
"connect.cassandra.kcql": "INSERT INTO students_topic SELECT id, name, age, timestamp_added FROM students PK timestamp_added INCREMENTALMODE=TIMESTAMP": the connector logic is to insert every row in a new topic message and use the column timestamp_added to check for new rows compared to the previous poll.

Once the connector is created successfully, you should see one message per row in the Cassandra table appearing in the target Apache Kafka students_topic topic.

tip

If your Aiven for Apache Kafka instance doesn't have the automatic creation of topic enabled, you might need to create the students_topic topic upfront before starting the connector

Prerequisites​

Setup an Apache Cassandra source connector with Aiven Console​

Define a Kafka Connect configuration file​

Create a Kafka Connect connector with the Aiven Console​

Example: Create a Cassandra source connector​

Prerequisites

Setup an Apache Cassandra source connector with Aiven Console

Define a Kafka Connect configuration file

Create a Kafka Connect connector with the Aiven Console

Example: Create a Cassandra source connector