'Promote a Read Replica to a standalone DB Instance.
:type id: str
:param id: Unique identifier for the new instance.
Must contain 1-63 alphanumeric characters.
First character must be a letter.
May not end with a hyphen or contain two consecutive hyphens
:type backup_retention_period: int
:param backup_retention_period: The number of days for which automated
backups are retained.  Setting this to
zero disables automated backups.
:type preferred_backup_window: str
:param preferred_backup_window: The daily time range during which
automated backups are created (if
enabled).  Must be in h24:mi-hh24:mi
format (UTC).
:rtype: :class:`boto.rds.dbinstance.DBInstance`
:return: The new db instance.'

def promote_read_replica(self, id, backup_retention_period=None, preferred_backup_window=None):

    params = {'DBInstanceIdentifier': id}
    if (backup_retention_period is not None):
        params['BackupRetentionPeriod'] = backup_retention_period
    if preferred_backup_window:
        params['PreferredBackupWindow'] = preferred_backup_window
    return self.get_object('PromoteReadReplica', params, DBInstance)
