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

def get_multi_instances_by_id(self, instance_ids):

    result = []
    for reservation in self.all_reservations():
        for instance in reservation.instances:
            if (instance.id in instance_ids):
                result.append(instance)
    if (instance_ids and (len(instance_ids) > len(result))):
        raise InvalidInstanceIdError(instance_ids)
    return result
