def get_primary_key(s3_index_row):
    """
    returns the primary key of the s3Index dynamo table.
    Args:
        s3_index_row(dict): dynamo table row for the s3Index

    Returns:
        (dict): primary key
    """
    primary = {"object-key": s3_index_row["object-key"],
               "version-node": s3_index_row["version-node"]}
    return primary