Open Stack

I'd like to open a discussion about bringing periodic auditing
to Glance. This would be very similar to Nova's instance usage audit,
which emits compute.instance.exists events for each instance that was
active for the given period. Likewise, Glance would emit an image.exists
for any image which was or is active for the given period.

As Ceilometer is the largest consumer of notifications in Openstack,
we'd really like to have their input on this.

Ceilometer is currently moving from a pulling/polling approach to a
push/notification based approach. The image.exists notification would be
useful for the 'image' metric seen in their docs here:

http://docs.openstack.org/developer/ceilometer/measurements.html#image-glance

Currently that meter tracks if the image (still) exists, and it does this
by setting the Gauge to 1 every time it gets a notification for the image.
The benefit of using a periodic image.exists notification for this meter
is that it would regularly get updated to ensure that the image is actually
still around.

As for Rackspace, the value we see in periodic image.exists is that it
provides a secondary way to identify usage. Currently, if you want to
track image usage using notifications, you must rely on instantaneous
notifications like image.create and image.delete. Going with those
notifications you'd bill for a given image until you receive an
image.delete. One issue that could arise would be a dropped image.delete.
Given that case, that image would be billed for indefinitely. With a
combination of instantaneous and periodic notification, you can detect
dropped notifications and in this case, a billing system using both
notifications would not end up over billing by charging for that image.

So, my question to the Ceilometer community is this, does this sound like
something Ceilometer would find value in and use? If so, would this be
something
we would want most deployers turning on?

Thanks,
Andrew Melton
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