[openstack-dev] [all] how to send messages (and events) to our users

Joshua Harlow harlowja at outlook.com
Wed Apr 8 22:14:21 UTC 2015

Sandy Walsh wrote:
> ________________________________________
>> From: Clint Byrum<clint at fewbar.com>
>> Sent: Wednesday, April 8, 2015 1:15 PM
>> There's this:
>> https://wiki.openstack.org/wiki/Cue
> Hmm, that looks interesting. Will read.
>> I also want to point out that what I'd actually rather see is that all
>> of the services provide functionality like this. Users would be served
>> by having an event stream from Nova telling them when their instances
>> are active, deleted, stopped, started, error, etc.
>> Also, I really liked Sandy's suggestion to use the notifications on the
>> backend, and then funnel them into something that the user can consume.
>> The project they have, yagi, for putting them into atom feeds is pretty
>> interesting. If we could give people a simple API that says "subscribe
>> to Nova/Cinder/Heat/etc. notifications for instance X, and put them
>> in an atom feed", that seems like something that would make sense as
>> an under-the-cloud service that would be relatively low cost and would
>> ultimately reduce load on API servers.
> Yes. It would be so good to pull apart the state-machine that is Nova and
> just emit completed actions via notifications. Then, have something like
> TaskFlow externalize the orchestration. Do away with RPC-over-AMQP.

Sounds good to me ;)

http://docs.openstack.org/developer/taskflow/notifications.html were 
designed for this purpose; some of the implementations at:


I know that http://www.rackspace.com/cloud/big-data/ is using one of 
these (among others) and using it to do various tracking of 
workflows/tasks, and such and gathering the information at whatever 
level is desired.

The neat thing is that it allows for post-workflow addition of listeners 
so if at some future point you want to know the timing of your workflow, 
well u can just plug another listener in that gathers this information 
(for example 


> And, anyone that is interested in the transitions can eavesdrop on the
> notifications.
> In our transition from StackTach.v2 to StackTach.v3 in production we simply
> cloned the notification feeds so the two systems can run in parallel*. No
> changes to OpenStack, no disruption of service. Later, we'll just kill off
> the v2 queues.
> -S
> * we did this in Yagi, since olso-messaging doesn't support multiple queues
> from one routing key.
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