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Hi,

As part of the Searchlight integration we need to extend our instance 
notifications with BDM data [1]. As far as I understand the main goal 
is to provide enough data about the instance to Searchlight so that 
Nova can use Searchlight to generate the response of the GET 
/servers/{server_id} requests based on the data stored in Searchlight.

I checked the server API response and I found one field that needs BDM 
related data: os-extended-volumes:volumes_attached. Only the uuid of 
the volume and the value of delete_on_terminate is provided in the API 
response.

I have two options about what to add to the InstancePayload and I want 
to get some opinions about which direction we should go with the 
implementation.

Option A: Add only the minimum required information from the BDM to the 
InstancePayload

  additional InstancePayload field:
      block_devices: ListOfObjectsField(BlockDevicePayload)

  class BlockDevicePayload(base.NotificationPayloadBase):
    fields = {
        'delete_on_termination': fields.BooleanField(default=False),
        'volume_id': fields.StringField(nullable=True),
    }

This payload would be generated from the BDMs connected to the instance 
where the BDM.destination_type == 'volume'.


Option B: Provide a comprehensive set of BDM attributes

  class BlockDevicePayload(base.NotificationPayloadBase):
    fields = {
        'source_type': fields.BlockDeviceSourceTypeField(nullable=True),
        'destination_type': fields.BlockDeviceDestinationTypeField(
                                nullable=True),
        'guest_format': fields.StringField(nullable=True),
        'device_type': fields.BlockDeviceTypeField(nullable=True),
        'disk_bus': fields.StringField(nullable=True),
        'boot_index': fields.IntegerField(nullable=True),
        'device_name': fields.StringField(nullable=True),
        'delete_on_termination': fields.BooleanField(default=False),
        'snapshot_id': fields.StringField(nullable=True),
        'volume_id': fields.StringField(nullable=True),
        'volume_size': fields.IntegerField(nullable=True),
        'image_id': fields.StringField(nullable=True),
        'no_device': fields.BooleanField(default=False),
        'tag': fields.StringField(nullable=True)
    }

In this case Nova would provide every BDM attached to the instance not 
just the volume ones.

I intentionally left out connection_info and the db id as those seems 
really system internal.
I also left out the instance related references as this 
BlockDevicePayload would be part of an InstancePayload which has an the 
instance uuid already.

What do you think, which direction we should go?

Cheers,
gibi


[1] 
https://blueprints.launchpad.net/nova/+spec/additional-notification-fields-for-searchlight