openstack 之 ceilometer: Notification

注：本文以ceilometer stable/kilo代码为例分析

ceilometer Notification实现架构

ceilometer Notification即是从消息队列中获取消息并将获取的消息转换成event事件（部分Notification生成sample）。ceilometer获取并存储Notification的结构图如下 ：

ceilometer获取的消息格式

通常，从消息队列中获取的消息格式如下：

{  '_context_roles': ['Member'],  '_context_request_id': 'req-ee35abb9-8bfd-48fa-9213',  '_context_quota_class': None,  'event_type': u'compute.instance.create.start',  '_context_service_catalog': [{    'endpoint': [{      'adminURL': 'http://127.0.0.1:8774/v2/tenant_id',      'region': 'RegionOne',       'id': '28d096fd6bf545e3b5de8a482de06d2d',       'internalURL': 'http://127.0.0.1:8774/v2/tenant_id',      'publicURL': 'http://127.0.0.1:8774/v2/tenant_id'    }],     'endpoints_links': [],    'type': 'compute',     'name': u'nova'}  }],  'timestamp': '2015-08-20 10:50:14.930752',   '_context_user': '329d6d053f83464a9f02e1cc9c560371',   '_context_auth_token': '1d05041c7b434f9c0ea95dccc',  '_context_user_id': '329d6d053f83464a9f02e1cc9c560371',    'payload': {},   '_context_read_deleted': 'no',  '_context_tenant': '079db7f7184c49ac94a5fb05a994904a',   '_context_is_admin': False,  '_context_project_id': '079db7f7184c49ac94a5fb05a994904a',   '_context_timestamp':  '2015-08-20T10:50:14.385672',  'publisher_id': 'aabbcc.ubuntu',  'message_id': '581f2ad8-40d7-468b-a692-733127ded3d4',   '_context_remote_address': u'127.0.0.1'}

消息的主图内容存放在payload中，一般从payload中可以取到消息对应的资源的一些信息。

ceilometer notification plugin

在ceilometer/agent/plugin_base.py中定义了Notification plugin的基础类，代码如下：

@six.add_metaclass(abc.ABCMeta)class NotificationBase(PluginBase):    """Base class for plugins that support the notification API."""    def __init__(self, transporter):        super(NotificationBase, self).__init__()        # NOTE(gordc): this is filter rule used by oslo.messaging to dispatch        # messages to an endpoint.        self.filter_rule = oslo_messaging.NotificationFilter(            event_type='|'.join(self.event_types))        self.transporter = transporter        # NOTE(gordc): if no publisher, this isn't a PipelineManager and        # data should be requeued.        self.requeue = False if hasattr(transporter, 'publisher') else True    @abc.abstractproperty    def event_types(self):        """Return a sequence of strings.        Strings are defining the event types to be given to this plugin.        """    def get_targets(self, conf):        """Return a sequence of oslo.messaging.Target.        Sequence is defining the exchange and topics to be connected for this        plugin.        :param conf: Configuration.        """        # TODO(sileht): Backwards compatibility, remove in J+2        if hasattr(self, 'get_exchange_topics'):            LOG.warn(_('get_exchange_topics API of NotificationPlugin is'                       'deprecated, implements get_targets instead.'))            targets = []            for exchange, topics in self.get_exchange_topics(conf):                targets.extend(oslo_messaging.Target(topic=topic,                                                     exchange=exchange)                               for topic in topics)            return targets    @abc.abstractmethod    def process_notification(self, message):        """Return a sequence of Counter instances for the given message.        :param message: Message to process.        """    def info(self, ctxt, publisher_id, event_type, payload, metadata):        """RPC endpoint for notification messages        When another service sends a notification over the message        bus, this method receives it.        :param ctxt: oslo.messaging context        :param publisher_id: publisher of the notification        :param event_type: type of notification        :param payload: notification payload        :param metadata: metadata about the notification        """        notification = messaging.convert_to_old_notification_format(            'info', ctxt, publisher_id, event_type, payload, metadata)        self.to_samples_and_publish(context.get_admin_context(), notification)    def to_samples_and_publish(self, context, notification):        """Return samples produced by *process_notification*.        Samples produced for the given notification.        :param context: Execution context from the service or RPC call        :param notification: The notification to process.        """        if self.requeue:            meters = [                utils.meter_message_from_counter(                    sample, cfg.CONF.publisher.telemetry_secret)                for sample in self.process_notification(notification)            ]            for notifier in self.transporter:                notifier.sample(context.to_dict(),                                event_type='ceilometer.pipeline',                                payload=meters)        else:            with self.transporter.publisher(context) as p:                p(list(self.process_notification(notification)))

基本上，只需要继承这个类，然后实现event_types、process_notification以及get_targets方法即可。event_types定义了过滤的事件类型，通过fnmatch匹配；
process_notification即为将notification处理成sample的格式；get_targets设置连接消息队列；
下面以compue为例介绍，ceilometer/compute/notifications/__init__py中定义如下：

class ComputeNotificationBase(plugin_base.NotificationBase):    @staticmethod    def get_targets(conf):        """Return a sequence of oslo.messaging.Target        This sequence is defining the exchange and topics to be connected for        this plugin.        """        return [oslo.messaging.Target(topic=topic,                                      exchange=conf.nova_control_exchange)                for topic in conf.notification_topics]

此处实现了get_targets方法，即设置nova中定义的的exchange并监听相关的设置队列。ceilometer/compute/notifications/instance.py中定义了具体的event_types、process_notification，代码实现如下

@six.add_metaclass(abc.ABCMeta)class UserMetadataAwareInstanceNotificationBase(        notifications.ComputeNotificationBase):    """Consumes notifications containing instance user metadata."""    def process_notification(self, message):        instance_properties = self.get_instance_properties(message)        if isinstance(instance_properties.get('metadata'), dict):            src_metadata = instance_properties['metadata']            del instance_properties['metadata']            util.add_reserved_user_metadata(src_metadata, instance_properties)        return self.get_sample(message)    def get_instance_properties(self, message):        """Retrieve instance properties from notification payload."""        return message['payload']    @abc.abstractmethod    def get_sample(self, message):        """Derive sample from notification payload."""class InstanceScheduled(UserMetadataAwareInstanceNotificationBase,                        plugin_base.NonMetricNotificationBase):    event_types = ['scheduler.run_instance.scheduled']    def get_instance_properties(self, message):        """Retrieve instance properties from notification payload."""        return message['payload']['request_spec']['instance_properties']    def get_sample(self, message):        yield sample.Sample.from_notification(            name='instance.scheduled',            type=sample.TYPE_DELTA,            volume=1,            unit='instance',            user_id=None,            project_id=message['payload']['request_spec']                              ['instance_properties']['project_id'],            resource_id=message['payload']['instance_id'],            message=message)class ComputeInstanceNotificationBase(        UserMetadataAwareInstanceNotificationBase):    """Convert compute.instance.* notifications into Samples."""    event_types = ['compute.instance.*']

除了要获取从消息队列中获取Notification存储外，还会通过event_types过滤出部分的事件，通过process_notification实现Notification->Smaple的转换。

ceilometer traits处理

在获取了notification之后，怎么处理这些event事件呢？ceilometer中提供了一个event_definations.yaml配置文件，在这个配置文件中，可以将Notification转换成按照event_definations.yaml中定义的格式，以compute事件为例，如下：

---- event_type: compute.instance.*  traits: &instance_traits    tenant_id:      fields: payload.tenant_id    user_id:      fields: payload.user_id    instance_id:      fields: payload.instance_id    host:      fields: publisher_id      plugin:        name: split        parameters:          segment: 1          max_split: 1    service:      fields: publisher_id      plugin: split    memory_mb:      type: int      fields: payload.memory_mb    disk_gb:      type: int      fields: payload.disk_gb    root_gb:      type: int      fields: payload.root_gb    ephemeral_gb:      type: int      fields: payload.ephemeral_gb    vcpus:      type: int      fields: payload.vcpus    instance_type_id:      type: int      fields: payload.instance_type_id    instance_type:      fields: payload.instance_type    state:      fields: payload.state    os_architecture:      fields: payload.image_meta.'org.openstack__1__architecture'    os_version:      fields: payload.image_meta.'org.openstack__1__os_version'    os_distro:      fields: payload.image_meta.'org.openstack__1__os_distro'    launched_at:      type: datetime      fields: payload.launched_at    deleted_at:      type: datetime      fields: payload.deleted_at- event_type: compute.instance.exists  traits:    <<: *instance_traits    audit_period_beginning:      type: datetime      fields: payload.audit_period_beginning    audit_period_ending:      type: datetime      fields: payload.audit_period_ending

event_type定义了符合匹配条件的event事件，traits定义从Notification中转换的数据。其中&resource_traits定义基础的traits项，<<: *resource_traits定义的是附加的traits项。
每个trait项由type、fields、plugin组成。type为可选项，默认是str，有datetime，int等可选；fields项，为从Notification获取的值，可以是数组；plugin项为调用已定义好的traits处理函数；

ceilometer Event格式及存储

将Notification根据event_definations.yaml处理完成后，生成的数据被定义成Event，格式如下：

{  message_id: “XXX”,   event_type: “compute.instance.create.end”,  timestamp: “yyyy-MM-dd mm-hh-ss”,  traits: [{key: ‘key’, value: ‘value’, type: ‘type’}……]}

Event查询

Ceilometer提供了Event事件查询的API接口，可以根据start_timestamp/end_timestamp，event_type/message_id查询Event事件。
如：

curl -X GET -H 'X-Auth-Token: ******' http://127.0.0.1:8774/v2/events?q.field=event_type&q.field=compute.instance.create.end

但实时上，event的这种存储方式比较的难用，如果想查询某个项目下的所有compute相关事件，实时上是非常难查询的，所以本人在实际开发中对event事件做了一些变动，以满足实际中按项目查询的需求。