Kafka Connectors are a crucial component in building scalable and fault-tolerant data pipelines. However, there are situations where you may need to reset the consumer offset, whether due to unexpected issues, changes in data schema, or other operational requirements. In this blog post, we will delve into the various aspects of resetting Kafka consumer offsets in Kafka Connectors.

Understanding Kafka Offsets

In Apache Kafka, offsets are markers that represent the position of a consumer in a topic. They define the last successfully processed message in a partition. Kafka Connectors use these offsets to keep track of data ingestion progress.

Scenarios Requiring Offset Reset

1. Data Schema Evolution

When the schema of your data evolves, you may need to reset the consumer offset to ensure that the new schema is correctly applied.

2. Re-processing Data

In certain scenarios, you might need to re-process data from the beginning due to errors, corrections, or updates in downstream systems.

3. Application Failures

If your Kafka Connector faces unexpected failures or issues, it might be necessary to reset the consumer offset to reprocess data from a known state.

Resetting Kafka Consumer Offsets

Step 1: Removing the Kafka Connector

To initiate the offset reset process, it’s essential to delete the Kafka Connector. Kafka imposes restrictions on resetting offsets when the consumer is in a stable state. Therefore, in the case of a connector, deletion serves as the appropriate action, unlike shutting down an application.

curl --location --request GET 'http://localhost:8083/connectors'

// Prints list of connector Eg. ['connector-1', 'connector-to-delete']

We will use the REST API provided by Confluent for this process.

Documentation: https://docs.confluent.io/platform/current/connect/references/restapi.html

curl --location --request DELETE 'http://localhost:8083/connectors/connector-to-delete/'

Congratulations!! The connector has been deleted

Step 2: Offset Reset Process

Once the connectors have been removed, proceed to reset the offset using the following command.

List Kafka consumers

kafka-consumer-groups  --list --bootstrap-server localhost:9092

Reset offset

kafka-consumer-groups --bootstrap-server localhost:9092 --group {consumerGroupName} --topic {topicName} --reset-offsets --to-earliest --execute

Following output will displayed on the console.

Group	TOPIC	PARTITION	OFFSET
{consumerGroupName}	{topicName}	0	0

Add the connectors again and voila, now the connectors will consume all the messages.

Considerations and Best Practices

1. Backup Existing Offsets:
   • Before resetting offsets, make sure to back up your existing offsets to avoid data loss or unintended consequences.
2. Impact Analysis:
   • Understand the impact of resetting offsets on downstream systems and consumers.
3. Testing:
   • Perform offset reset operations in a controlled environment first to identify and mitigate any potential issues.
4. Documentation:
   • Keep detailed documentation about when and why offset resets are performed.