OpenStack快照分析：（三）从磁盘启动云主机离线(在线)快照分析

磁盘启动云主机离线(在线)快照

1.1.   nova-api处理过程

磁盘启动的云主机在做离线快照时，还是首先是nova-api接收请求，函数入口和前述一样，还是 nova/api/openstack/compute/servers.py/ServersController._action_create_image，下面一起来看看：

@wsgi.response(202)
@extensions.expected_errors((400, 403, 404, 409))
# 定义关联的API接口
@wsgi.action('createImage')
@common.check_snapshots_enabled
@validation.schema(schema_servers.create_image, '2.0', '2.0')
@validation.schema(schema_servers.create_image, '2.1')
def _action_create_image(self, req, id, body):
    """Snapshot a server instance."""
    # 从req中获取请求的上下文，并验证执行权限
    context = req.environ['nova.context']
    context.can(server_policies.SERVERS % 'create_image')

    # 从body中解析出传递的参数，快照名称及属性信息
    entity = body["createImage"]
    image_name = common.normalize_name(entity["name"])
    metadata = entity.get('metadata', {})
    snapshot_id = entity.get("snapshot_id", None)

    # Starting from microversion 2.39 we don't check quotas on createImage
    if api_version_request.is_supported(req, max_version=api_version_request.MAX_IMAGE_META_PROXY_API_VERSION):
        # 检查快照属性的相关配置信息
        common.check_img_metadata_properties_quota(context, metadata)
   
    instance = self._get_server(context, req, id)

    snapshot = snapshot_current(context, instance, self.compute_rpcapi)
    if snapshot:  # if there are snapshots, then create an image with snashots.
        if not snapshot_id:
            snapshot_id = snapshot["id"]
        image = snapshot_create_image(context, snapshot_id, instance, self.compute_rpcapi, entity)
    else:
        #从数据库中获取实例对象（InstanceV2）及块设备映射列表
        bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(context, instance.uuid)

        # 判断实例是镜像启动还是磁盘启动
        if compute_utils.is_volume_backed_instance(context, instance, bdms):
            # 校验执行权限
            context.can(server_policies.SERVERS % 'create_image:allow_volume_backed')
            # 这里执行的是磁盘启动方式的快照，传递的参数包括：
            # 1、关于权限的上下文context
            # 2、虚拟机的实例对象instance
            # 3、快照的名称image_name
            # 本章节讲的磁盘启动的云主机快照就是进入该分支进行操作。
            image = self.compute_api.snapshot_volume_backed(context, instance, image_name, extra_properties=metadata)
        else:
            # 这里是镜像启动的云主机快照的入口，即上节内容。
            image = self.compute_api.snapshot(context, instance, image_name, extra_properties=metadata)

    if api_version_request.is_supported(req, '2.45'):
        return {'image_id': image['id']}

    # build location of newly-created image entity
    image_id = str(image['id'])
    image_ref = glance.generate_image_url(image_id)

    resp = webob.Response(status_int=202)
    resp.headers['Location'] = image_ref
    return resp