[openstack-dev] [nova] [notification] BlockDeviceMapping in InstancePayload

John Garbutt john at johngarbutt.com
Wed Mar 15 12:44:50 UTC 2017

On 13 March 2017 at 17:14, Balazs Gibizer <balazs.gibizer at ericsson.com> wrote:
> 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.

+1 leaving those out.

> What do you think, which direction we should go?

There are discussions around extending the info we give out about BDMs
in the API.

What about in between, list all types of BDMs, so include a touch more
info so you can tell which one is a volume for sure.

  class BlockDevicePayload(base.NotificationPayloadBase):
    fields = {
        'destination_type': fields.BlockDeviceDestinationTypeField(
                               nullable=True), # Maybe just called "type"?
        'boot_index': fields.IntegerField(nullable=True),
        'device_name': fields.StringField(nullable=True), # do we
ignore that now?
        'delete_on_termination': fields.BooleanField(default=False),
        'volume_id': fields.StringField(nullable=True),
        'tag': fields.StringField(nullable=True)


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