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
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