1.1.nova-api處理過程

磁碟啟動的雲主機在做離線快照時，還是首先是nova-api接收請求，函式入口和前述一樣，還是nova/api/openstack/compute/servers.py/ServersController._action_create_image，下面一起來看看：

@wsgi.response(202) @extensions.expected_errors((400, 403, 404, 409)) # 定義關聯的API介面 @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.""" # 從req中獲取請求的上下文，並驗證執行許可權context = req.environ['nova.context'] context.can(server_policies.SERVERS % 'create_image') # 從body中解析出傳遞的引數，快照名稱及屬性資訊 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): # 檢查快照屬性的相關配置資訊 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: #從資料庫中獲取例項物件（InstanceV2）及塊裝置對映列表 bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(context, instance.uuid) # 判斷例項是映象啟動還是磁碟啟動if compute_utils.is_volume_backed_instance(context, instance, bdms): # 校驗執行許可權 context.can(server_policies.SERVERS % 'create_image:allow_volume_backed') # 這裡執行的是磁碟啟動方式的快照，傳遞的引數包括： # 1、關於許可權的上下文context # 2、虛擬機器的例項物件instance # 3、快照的名稱image_name # 本章節講的磁碟啟動的雲主機快照就是進入該分支進行操作。 image = self.compute_api.snapshot_volume_backed(context, instance, image_name, extra_properties=metadata) else: # 這裡是映象啟動的雲主機快照的入口，即上節內容。 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

可以看到，執行磁碟啟動雲主機快照時，實際走的是“compute_api.snapshot_volume_backed”，下面對這部分程式碼具體分析，程式碼位置：nova/compute/api.py/API.snapshot_volume_backed：

@check_instance_state(vm_state=[vm_states.ACTIVE, vm_states.STOPPED, vm_states.SUSPENDED]) def snapshot_volume_backed(self, context, instance, name, extra_properties=None): """Snapshot the given volume-backed instance.從例項的system_metadata生成映象屬性（排除不可繼承屬性），如下：# { #u'min_disk': u'20', #'is_public': False, #'min_ram': u'0', #'properties': { #'base_image_ref': u'' #}, #'name': u'snapshot1' # }

:param instance: nova.objects.instance.Instance object :param name: name of the backup or snapshot :param extra_properties: dict of extra image properties to include :returns: the new image metadata """ # 獲取例項的metadata屬性image_meta = self._initialize_instance_snapshot_metadata(instance, name, extra_properties)image_meta['size'] = 0 # 清除映象metadata屬性中的container_format，disk_forma屬性for attr in ('container_format', 'disk_format'): image_meta.pop(attr, None) properties = image_meta['properties'] # clean properties before filling，清除properties屬性裡面的'block_device_mapping', 'bdm_v2', 'root_device_name'相關屬性值for key in ('block_device_mapping', 'bdm_v2', 'root_device_name'): properties.pop(key, None) # 將例項中的‘root_device_name’屬性更新到properties屬性裡，image_meta的最終內容如： # { #'name': u'snapshot1', #u'min_ram': u'0', #u'min_disk': u'20', #'is_public': False, #'properties': { #u'base_image_ref': u'', #'root_device_name': u'/dev/vda' #}, #'size': 0 # }if instance.root_device_name: properties['root_device_name'] = instance.root_device_name # 從資料庫中獲取該雲主機所關聯的所有塊裝置，結果會返回一個BlockDeviceMappingList物件 bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(context, instance.uuid) # 接下來開始做快照的操作，注意，雲主機掛在了多少個卷裝置，就要做多少次快照 mapping = []# list of BDM dicts that can go into the image properties # Do some up-front filtering of the list of BDMs from # which we are going to create snapshots. volume_bdms = [] for bdm in bdms: if bdm.no_device: # 對映關係中沒有塊裝置，則忽略此條對映continue if bdm.is_volume: # These will be handled below.此對映包含塊裝置，加入到volume_bdms，準備做快照volume_bdms.append(bdm) else: mapping.append(bdm.get_image_mapping()) # Check limits in Cinder before creating snapshots to avoid going over # quota in the middle of a list of volumes. This is a best-effort check # but concurrently running snapshot requests from the same project # could still fail to create volume snapshots if they go over limit. # 在建立快照之前，需要首先在Cinder中檢查配額限制，以避免超過配額限制if volume_bdms: limits = self.volume_api.get_absolute_limits(context) total_snapshots_used = limits['totalSnapshotsUsed'] max_snapshots = limits['maxTotalSnapshots'] # -1 means there is unlimited quota for snapshots if (max_snapshots > -1 and len(volume_bdms) + total_snapshots_used > max_snapshots): LOG.debug('Unable to create volume snapshots for instance. Currently has %s snapshots, requesting %s new snapshots, with a limit of %s.', total_snapshots_used, len(volume_bdms), max_snapshots, instance=instance) raise exception.OverQuota(overs='snapshots') quiesced = False # 判斷虛擬機器的狀態，如果虛擬機器處於active，則通過rpc通知虛擬機器進入靜默狀態（異常處理省略）if instance.vm_state == vm_states.ACTIVE: LOG.info("Attempting to quiesce instance before volume snapshot.", instance=instance) self.compute_rpcapi.quiesce_instance(context, instance) quiesced = True # 定義一個獲取雲主機上的及具體卷資訊的方法，返回雲主機的卷對映 @wrap_instance_event(prefix='api') def snapshot_instance(self, context, instance, bdms): for bdm in volume_bdms: # create snapshot based on volume_id #根據卷的volume_id從資料庫獲取卷的詳細資訊volume = self.volume_api.get(context, bdm.volume_id) # 組裝出一個貌似是desc的消息，比如快照名稱是snapshot1，則這裡就是snapshot for snapshot1name = _('snapshot for %s') % image_meta['name'] LOG.debug('Creating snapshot from volume %s.', volume['id'], instance=instance) # 呼叫cinder的api create_snapshot_force建立新的卷# 在“create_snapshot_force”中實際上是通過cinderclient來呼叫volume_snapshots.create # 來發起建立卷的請求，具體是由cinder-volume來完成卷的快照，返回的內容為卷快照的資訊， # 格式如： #{

#'status': u'creating', #'display_name': u'snapshot for snapshot1', #'created_at': u'2016-06-24T09:23:00.517279', #'display_description': u'', #'volume_size': 20, #'volume_id': u'60e16af2-0684-433c-a1b6-c1af1c2523fc', #'progress': None, #'project_id': u'25520b29dce346d38bc4b055c5ffbfcb', #'id': u'cede2421-ea68-4a8e-937d-c27074b9024b', #'size': 20 # } snapshot = self.volume_api.create_snapshot_force( context, volume['id'], name, volume['display_description']) # 接著會根據bdm資訊，來構建快照的dict格式屬性資訊，返回一個BlockDeviceDict物件，屬性如下: # { #'guest_format': None, #'boot_index': 0, #'no_device': None, #'connection_info': None, #'snapshot_id': u'cede2421-ea68-4a8e-937d-c27074b9024b', #'volume_size': 20, #'device_name': u'/dev/vda', #'disk_bus': u'virtio', #'image_id': None, #'source_type': 'snapshot', #'device_type': u'disk', #'volume_id': None, #'destination_type': 'volume', #'delete_on_termination': False # } mapping_dict = block_device.snapshot_from_bdm(snapshot['id'], bdm) # 過濾掉已經在資料庫中存在的欄位 mapping_dict = mapping_dict.get_image_mapping() # 將雲主機所有的對映關係都新增到mapping中 mapping.append(mapping_dict) return mapping self._record_action_start(context, instance, instance_actions.CREATE_IMAGE) # 呼叫“snapshot_instance”，獲取雲主機所有的mapping關係 mapping = snapshot_instance(self, context, instance, bdms) # 如果此時卷的檔案系統已靜默，這裡則進行解凍處理，實現過程就是通過rpc.case傳送非同步請求給nova-compute # nova-compute接收到訊息後，會等到快照完成後對檔案系統進行解凍（需要agent支援）if quiesced: self.compute_rpcapi.unquiesce_instance(context, instance, mapping) # 更新雲主機metadata資訊中的properties資訊if mapping: properties['block_device_mapping'] = mapping properties['bdm_v2'] = True # 到這一步時，會到新增一條記錄到glance快照（映象）資料庫條目 #（會在Dashboard的映象面板顯示一條名為snapshot1的快照記錄)， # 快照的大部分資訊都拷貝至系統盤屬性，這是因為卷快照是可以直接用來啟動雲主機的， # 另外'block_device_mapping'屬性中包含所有的volume裝置快照資訊（如果有的話）， # 每個volume裝置快照資訊作為一條記錄，記錄在image_properties資料表； # { 'name': u'snapshot1', 'min_ram': u'0', 'min_disk': u'20', 'is_public': False, 'properties': { 'bdm_v2': True, 'block_device_mapping': [{ 'guest_format': None, 'boot_index': 0, 'no_device': None, 'image_id': None, 'volume_id': None, 'device_name': u'/dev/vda', 'disk_bus': u'virtio', 'volume_size': 20, 'source_type': 'snapshot', 'device_type': u'disk', 'snapshot_id': u'cede2421-ea68-4a8e-937d-c27074b9024b', 'destination_type': 'volume', 'delete_on_termination': False }], 'base_image_ref': u'', 'root_device_name': u'/dev/vda' }, 'size': 0 } return self.image_api.create(context, image_meta)

最後一步通過呼叫image_api的create來建立image，跟蹤過去實際上就只有一句“session.create(context, image_info, data=data)”，呼叫RESTful API來建立image。

至此，nova-api的工作已經做完，總結一下，nov-api主要是 完成了一下工作：

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