def get_multi_instances_by_id(self, instance_ids):
        """
        :param instance_ids: A string list with instance ids
        :return: A list with instance objects
        """
        result = []

        for reservation in self.all_reservations():
            for instance in reservation.instances:
                if instance.id in instance_ids:
                    result.append(instance)

        # TODO: Trim error message down to specific invalid id.
        if instance_ids and len(instance_ids) > len(result):
            raise InvalidInstanceIdError(instance_ids)

        return result
:param instance_ids: A string list with instance ids
        :return: A list with instance objects