[openstack-dev] [nova] Host maintenance notification

Matt Riedemann mriedem at linux.vnet.ibm.com
Mon Apr 6 18:17:20 UTC 2015

On 4/6/2015 9:46 AM, Chris Friesen wrote:
> On 04/06/2015 07:56 AM, Ed Leafe wrote:
>> On Apr 6, 2015, at 1:21 AM, Chris Friesen <chris.friesen at windriver.com>
>> wrote:
>>>> Please feel free to add a blueprint in Launchpad. I don't see this as
>>>> needing a full spec, really. It shouldn't be more than a few lines of
>>>> code to send a new notification message.
>>> Wouldn't a new notification message count as an API change?  Or are we
>>> saying that it's such a small API change that any discussion can
>>> happen in
>>> the blueprint?
>> I don't think that the notification system is the same as the API. It is
>> something that you can subscribe to or not, and is distinct from the API.
> It's certainly not the same as the REST API.  I think an argument could
> be made that the notification system is part of the API, where API is
> defined more generally as "something that expresses a software component
> in terms of its operations, inputs, outputs, and underlying types".
> If we don't exercise any control over the contents of the notifications
> messages, that would make it difficult for consumers of the
> notifications to do anything interesting with them.  At a minimum it
> might make sense to do something like REST API microversions, with a
> version number and a place to look up what changed with each version.
> Chris
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The events and their payloads are listed in the wiki here [1].

In the past people have added new notifications with just bug reports, 
I'm not sure a new spec is required for a host going into maintenance 
mode (as long as it's new and not changing something).

And yes, we have to be careful about making changes to existing 
notifications (the event name or the payload) since we have to treat 
them like APIs, but (1) they aren't versioned today and (2) we don't 
have any kind of integration testing on the events that I'm aware of, 
unless it's through something like ceilometer trying to do something 
with them in a tempest scenario test, but I doubt that.

[1] https://wiki.openstack.org/wiki/SystemUsageData



Matt Riedemann

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