def METHOD_NAME(cluster_id, emr_client):
    """
    Terminates a cluster. This terminates all instances in the cluster and cannot
    be undone. Any data not saved elsewhere, such as in an Amazon S3 bucket, is lost.
    :param cluster_id: The ID of the cluster to terminate.
    :param emr_client: The Boto3 EMR client object.
    """
    try:
        emr_client.terminate_job_flows(JobFlowIds=[cluster_id])
        logger.info("Terminated cluster %s.", cluster_id)
    except ClientError:
        logger.exception("Couldn't terminate cluster %s.", cluster_id)
        raise