nova-compute charm should use unversioned notification format

[Nusrath Mohammed]

nova-compute charm needs a variable to set notification_format (both, versioned, unversioned)

Nova currently generates versioned_notifications that have no consumer, ideally going forward Ceilometer should be able to consume this queue but there seems to be a wishlist bug: https://bugs.launchpad.net/ceilometer/+bug/1665449

By default, notification_format is set to both and hence the charm needs a feature to set this variable to unversioned until the versioned_notifications can be consumed by ceilometer.

[James Page (james-page)]

I think we know what format should be used, so providing a configuration option makes little sense; lets just set the right values in the nova.conf templates for each supported release; when ceilometer does support the versioned format, we can just switch back to 'both'.

[James Page (james-page)]

Which release does this impact from?

[Craige McWhirter (craige)]

The need for this feature, for myself at least is related to this bug:

https://bugs.launchpad.net/ceilometer/+bug/1665449

Which we are now hitting on production clouds using charm versions >= 17.11

There are three options that can be set for "notification_format" in [oslo_messaging_notifications]:

['unversioned', 'versioned', 'both']

Of which 'both' is the default

https://github.com/openstack/nova/blob/stable/pike/nova/conf/notifications.py#L88-L105

As there is no consumer, I'd be inclined to set "unversioned" as the default until LP#1665449 is resolved.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Craige McWhirter (<email address hidden>) on branch: master
Review: https://review.openstack.org/559272
Reason: Deferring to an opinionated stance on the setting.