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not familiar/smart enough to comment on design within Nova but i'm very 
much in favour if this is possible. the polling option in Ceilometer was 
always a means to get information not readily available via notifications.

that said, i don't think we can completely do away with polling. i'm 
aware of some cases where in addition to polling for measurements, some 
users leverage the polling agent as a means of performing health checks 
as well but the less load our polls generate the better.

On 17/06/2015 11:52 AM, Matt Riedemann wrote:
> Without getting into the details from the etherpad [1], a few of us in 
> IRC today were talking about how the ceilometer compute-agent polls 
> libvirt directly for guest VM statistics and how ceilometer should 
> really be getting this information from nova via notifications sent 
> from a periodic task in the nova compute manager.
>
> Nova already has the get_instance_diagnostics virt driver API which is 
> nice in that it has structured versioned instance diagnostic 
> information regardless of virt driver (unlike the v2 
> os-server-diagnostics API which is a free-form bag of goodies 
> depending on which virt driver is used, which makes it mostly 
> untestable and not portable).  The problem is the 
> get_instance_diagnostics virt driver API is per-instance, so it's not 
> efficient in the case that you want bulk instance data for a given 
> compute host.
>
> So the idea is to add a new virt driver API to get the bulk data and 
> emit that via a structured versioned payload similar to 
> get_instance_diagnostics but for all instances.
>
> Eventually the goal is for nova to send what ceilometer is collecting 
> today [2] and then ceilometer can just consume that notification 
> rather than doing the direct hypervisor polling it has today.
>
> Anyway, this is the high level idea, the details/notes are in the 
> etherpad along with next steps.
>
> Feel free to chime in now with reasons why this is crazy and will 
> never work and we shouldn't waste our time on it.
>
> [1] https://etherpad.openstack.org/p/nova-hypervisor-bulk-stats-notify
> [2] 
> http://docs.openstack.org/admin-guide-cloud/content/section_telemetry-compute-meters.html
>

-- 
gord