Notifications¶
Ironic notifications are events intended for consumption by external services like a billing or usage system, a monitoring data store, or other OpenStack services. Notifications are sent to these services over a message bus by oslo.messaging’s Notifier class [1]. The consumer sees the notification as a JSON object structured in the following way as defined by oslo.messaging:
{
"priority": <string, defined by the sender>,
"event_type": <string, defined by the sender>,
"timestamp": <string, the isotime of when the notification emitted>,
"publisher_id": <string, defined by the sender>,
"message_id": <uuid, generated by oslo>,
"payload": <json serialized dict, defined by the sender>
}
Versioned notifications in ironic¶
To make it easier for consumers of ironic’s notifications to use predictably, ironic defines each notification and its payload as oslo versioned objects [2].
An increase in the minor version of the payload will indicate that only new fields have been added since the last version, so the consumer can still use the notification as it did previously. An increase in the major version of the payload indicates that the consumer can no longer parse the notification as it did previously, indicating that a field was removed or the type of the payload field changed.
Ironic exposes a configuration option in the DEFAULT
section called
notification_level
that indicates the minimum level for which
notifications will be emitted. This option is not defined by default, which
indicates that no notifications will be sent by ironic. Notification levels
may be “debug”, “info”, “warning”, “error”, or “critical”, and each
level follows the OpenStack logging guidelines [3]. If it’s desired that
ironic emit all notifications, the config option should be set to “debug”, for
example. If only “warning”, “error”, and “critical” notifications are needed,
the config option should be set to “warning”. This level gets exposed in the
notification on the wire as the “priority” field.
All ironic versioned notifications will be sent on the message bus via the
ironic_versioned_notifications
topic.
Ironic also has a set of base classes that assist in clearly defining the notification itself, the payload, and the other fields not auto-generated by oslo (level, event_type and publisher_id). Below describes how to use these base classes to add a new notification to ironic.
Adding a new notification to ironic¶
To add a new notification to ironic, new versioned notification classes should be created by subclassing the NotificationBase class to define the notification itself and the NotificationPayloadBase class to define which fields the new notification will contain inside its payload. You may also define a schema to allow the payload to be automatically populated by the fields of an ironic object. Here’s an example:
# The ironic object whose fields you want to use in your schema
@base.IronicObjectRegistry.register
class ExampleObject(base.IronicObject):
# Version 1.0: Initial version
VERSION = '1.0'
fields = {
'id': fields.IntegerField(),
'uuid': fields.UUIDField(),
'a_useful_field': fields.StringField(),
'not_useful_field': fields.StringField()
}
# A class for your new notification
@base.IronicObjectRegistry.register
class ExampleNotification(notification.NotificationBase):
# Version 1.0: Initial version
VERSION = '1.0'
fields = {
'payload': fields.ObjectField('ExampleNotifPayload')
}
# A class for your notification's payload
@base.IronicObjectRegistry.register
class ExampleNotifPayload(notification.NotificationPayloadBase):
# Schemas are optional. They just allow you to reuse other objects'
# fields by passing in that object and calling populate_schema with
# a kwarg set to the other object.
SCHEMA = {
'a_useful_field': ('example_obj', 'a_useful_field')
}
# Version 1.0: Initial version
VERSION = '1.0'
fields = {
'a_useful_field': fields.StringField(),
'an_extra_field': fields.StringField(nullable=True)
}
SCHEMA defines how to populate the payload fields. It’s an optional attribute that subclasses may use to easily populate notifications with data from other objects.
It is a dictionary where every key value pair has the following format:
<payload_field_name>: (<data_source_name>,
<field_of_the_data_source>)
The <payload_field_name>
is the name where the data will be stored in the
payload object; this field has to be defined as a field of the payload.
The <data_source_name>
shall refer to name of the parameter passed as
kwarg to the payload’s populate_schema()
call and this object will be
used as the source of the data. The <field_of_the_data_source>
shall be
a valid field of the passed argument.
The SCHEMA needs to be applied with the populate_schema()
call before the
notification can be emitted.
The value of the payload.<payload_field_name>
field will be set by the
<data_source_name>.<field_of_the_data_source>
field. The
<data_source_name>
will not be part of the payload object internal or
external representation.
Payload fields that are not set by the SCHEMA can be filled in the same way as in any versioned object.
Then, to create a payload, you would do something like the following. Note
that if you choose to define a schema in the SCHEMA class variable, you must
populate the schema by calling populate_schema(example_obj=my_example_obj)
before emitting the notification is allowed:
my_example_obj = ExampleObject(id=1,
a_useful_field='important',
not_useful_field='blah')
# an_extra_field is optional since it's not a part of the SCHEMA and is a
# nullable field in the class fields
my_notify_payload = ExampleNotifyPayload(an_extra_field='hello')
# populate the schema with the ExampleObject fields
my_notify_payload.populate_schema(example_obj=my_example_obj)
You then create the notification with the oslo required fields (event_type, publisher_id, and level, all sender fields needed by oslo that are defined in the ironic notification base classes) and emit it:
notify = ExampleNotification(
event_type=notification.EventType(object='example_obj',
action='do_something', phase='start'),
publisher=notification.NotificationPublisher(service='conductor',
host='cond-hostname01'),
level=fields.NotificationLevel.DEBUG,
payload=my_notify_payload)
notify.emit(context)
This will send the following notification over the message bus:
{
"priority": "debug",
"payload":{
"ironic_object.namespace":"ironic",
"ironic_object.name":"ExampleNotifyPayload",
"ironic_object.version":"1.0",
"ironic_object.data":{
"a_useful_field":"important",
"an_extra_field":"hello"
}
},
"event_type":"baremetal.example_obj.do_something.start",
"publisher_id":"conductor.cond-hostname01"
}
[1] | http://docs.openstack.org/developer/oslo.messaging/notifier.html |
[2] | http://docs.openstack.org/developer/oslo.versionedobjects |
[3] | https://wiki.openstack.org/wiki/LoggingStandards#Log_level_definitions |