(An S3 source connector named s3-connector stopped running.

According to the official Apache Kafka Connect REST API documentation, restarting a connector can be done at different granularities: connector-level, task-level, or both. By default, calling POST /connectors/{name}/restart only restarts the connector instance, not its tasks.

To restart the connector and all of its tasks, the request must explicitly include the query parameter includeTasks=true. This instructs Kafka Connect to restart the connector and all associated tasks, regardless of whether they are currently running or failed.

Option B (onlyFailed=true) limits the restart to only failed tasks, which does not meet the requirement to restart all tasks. Option C restarts only the connector instance, leaving tasks untouched. Option D restarts a single specific task and does not restart the connector itself.

Therefore, the correct and officially documented REST request to restart the connector instance and all tasks is:

POST /connectors/s3-connector/restart?includeTasks=true

This ensures a full restart of the connector and its execution context across the Kafka Connect cluster.