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Hi,

We would like to be notified once an alarm state is changed, so we prefer using the message bus. 
As far as I understand, ceilometer and aodh APIs do not provide immediate notifications. If we use the APIs, we will have to poll the data periodically and look for changes, and we will get them in delay. By listening to the message bus we can get the notifications immediately, like we do with other openstack components. 

Is there an advantage in using the API instead? 
And what do you mean by "aggregation on events data"? what kind of aggregations can we do?

Thanks,
Ifat.

> -----Original Message-----
> From: liusheng [mailto:liusheng1175 at 126.com]
> Sent: Wednesday, January 06, 2016 10:10 AM
> 
> Hi Ifat,
> 
> what way do you want to use the alarm change notifications? using
> events from Ceilometer API or directly collecting the notifications
> from message bus?
> if we configure Ceilometer to listen the notifications from aodh, the
> notifications about alarm changes will be converted to events and
> stored in Ceilometer storage. if you want to use the events about alarm
> changes, the same info can be queried by "alarm-history" API, may be
> you want to do aggregation on events data ?
> 
> Thanks
> Liu sheng
> 
> 在 2016/1/5 21:37, AFEK, Ifat (Ifat) 写道:
> >> -----Original Message-----
> >> From: gord chung [mailto:gord at live.ca]
> >> Sent: Friday, December 11, 2015 10:17 PM
> >>
> >> the original reason this was implemented i believe was to track
> alarm
> >> state changes as an event in ceilometer events. i still see this as
> a
> >> valid use case but it does duplicate some of the functionality of
> >> alarm history.
> >>
> >> i think the main items are to not flood the message bus with
> messages
> >> that no one is listening to. but if there is a use case for it, i'm
> >> happy to see it remain (and improved).
> >>
> >> you can check the patch that Liusheng referenced, but the basic
> >> concept is as mentioned: send message when an alarm state is
> changed.
> >>
> > Hi Gord,
> >
> > We had some further discussions about this issue in Vitrage team, and
> we decided we do want to use Aodh notifications about alarm state
> changes.
> >
> > One reason is that we want to be notified about every alarm, yet we
> don't want to register our web-hook on each alarm definition
> separately. The other reason is that we already listen to message bus
> notifications of other openstack components (like nova), and we would
> like to handle aodh notifications the same way we handle all other
> openstack notifications.
> >
> > We will be happy if this code remains.
> >
> > Thanks,
> > Ifat.