def get_s3_index_arn(bosslet_config):
    """
    Get arn of the DynamoDB s3 index.

    Args:
        bosslet_config (BossConfiguration): target bosslet

    Returns:
        (str):
    """
    names = bosslet_config.names
    dynamo = bosslet_config.session.client('dynamodb')
    resp = dynamo.describe_table(TableName=names.s3_index.ddb)
    return resp['Table']['TableArn']