虛擬機冷遷移和resize代碼分析（一）

#  1、冷遷移和resize

　　遷移是指將虛擬機從一個計算節點遷移到另一個節點上。冷遷移是相對熱遷移而言，區別在於冷遷移過程當中虛擬機時關機或者是處於不可用的狀態，而熱遷移則須要保證虛擬機時刻運行。    　　Resize則是根據需求從新調整虛擬機的計算能力和資源。Resize和冷遷移的工做流程相同，區別只是Resize時必須保持新的Flavor配置大於舊的配置，而冷遷移則要求二者相同。Resize的工做流程如圖所示：

1.resize過程

　　nova-api在收到虛擬機resize的請求後，會去調用/nova/api/openstack/compute/servers.py中的_action_resize()方法，部分代碼和註釋以下： 

    @wsgi.response(202)     @extensions.expected_errors((400, 401, 403, 404, 409))     @wsgi.action('resize')     @validation.schema(schema_server_resize)     def _action_resize(self, req, id, body):         """Resizes a given instance to the flavor size requested."""         resize_dict = body['resize']         #獲取升級flavor         flavor_ref = str(resize_dict["flavorRef"])

        resize_kwargs = {}

        if list(self.resize_extension_manager):             self.resize_extension_manager.map(self._resize_extension_point,                                               resize_dict, resize_kwargs)

        self._resize(req, id, flavor_ref, **resize_kwargs)

　　接着調用_resize()方法，部分代碼和註釋以下：

    def _resize(self, req, instance_id, flavor_id, **kwargs):         """Begin the resize process with given instance/flavor."""         context = req.environ["nova.context"]         authorize(context, action='resize')         #經過instance_id獲取虛擬機實例的具體信息         instance = self._get_server(context, req, instance_id)

        try:             #傳遞instance和flavor_id兩個參數             self.compute_api.resize(context, instance, flavor_id, **kwargs)         except exception.InstanceUnknownCell as e:             raise exc.HTTPNotFound(explanation=e.format_message())         except exception.QuotaError as error:             raise exc.HTTPForbidden(                 explanation=error.format_message())         except exception.FlavorNotFound:             msg = _("Unable to locate requested flavor.")             raise exc.HTTPBadRequest(explanation=msg)         except exception.CannotResizeToSameFlavor:             msg = _("Resize requires a flavor change.")             raise exc.HTTPBadRequest(explanation=msg)         except (exception.CannotResizeDisk,                 exception.AutoDiskConfigDisabledByImage) as e:             raise exc.HTTPBadRequest(explanation=e.format_message())         except exception.InstanceIsLocked as e:             raise exc.HTTPConflict(explanation=e.format_message())         except exception.InstanceInvalidState as state_error:             common.raise_http_conflict_for_instance_invalid_state(state_error,                     'resize', instance_id)         except exception.ImageNotAuthorized:             msg = _("You are not authorized to access the image "                     "the instance was started with.")             raise exc.HTTPUnauthorized(explanation=msg)         except exception.ImageNotFound:             msg = _("Image that the instance was started "                     "with could not be found.")             raise exc.HTTPBadRequest(explanation=msg)         except (exception.NoValidHost,                 exception.AutoDiskConfigDisabledByImage) as e:             raise exc.HTTPBadRequest(explanation=e.format_message())         except exception.Invalid:             msg = _("Invalid instance image.")             raise exc.HTTPBadRequest(explanation=msg)

2.冷遷移過程

　　nova-api在收到虛擬機冷遷移的請求後，會去調用/nova/api/openstack/compute/migrate_server.py中的_migrate()方法，部分代碼和註釋以下： 

    @wsgi.response(202)     @extensions.expected_errors((400, 403, 404, 409))     @wsgi.action('migrate')     def _migrate(self, req, id, body):         """Permit admins to migrate a server to a new host."""         context = req.environ['nova.context']         authorize(context, action='migrate')         #得到虛擬機信息         instance = common.get_instance(self.compute_api, context, id)         try:             #僅傳遞instance一個參數             self.compute_api.resize(req.environ['nova.context'], instance)         except (exception.TooManyInstances, exception.QuotaError) as e:             raise exc.HTTPForbidden(explanation=e.format_message())         except exception.InstanceIsLocked as e:             raise exc.HTTPConflict(explanation=e.format_message())         except exception.InstanceInvalidState as state_error:             common.raise_http_conflict_for_instance_invalid_state(state_error,                     'migrate', id)         except exception.InstanceNotFound as e:             raise exc.HTTPNotFound(explanation=e.format_message())         except exception.NoValidHost as e:             raise exc.HTTPBadRequest(explanation=e.format_message())

　　從上面的分析能夠看出，冷遷移和resize底層接口一致，假如前端傳入了新的flavor，則是resize，新的flavor被傳入底層。遷移時傳入底層的flavor則爲自身實例相同的flavor。底層根據傳入的flavor參數執行相同的邏輯。resize和冷遷移的區別是在遷移的同時，是否改變虛擬機的flavor。 後面將繼續介紹二者底層相同的調用邏輯。