[openstack-dev] [nova] Host maintenance notification

Matt Riedemann mriedem at linux.vnet.ibm.com
Tue Apr 7 17:07:22 UTC 2015

On 4/6/2015 2:07 PM, Chris Friesen wrote:
> On 04/06/2015 12:52 PM, Matthew Treinish wrote:
>> On Mon, Apr 06, 2015 at 01:17:20PM -0500, Matt Riedemann wrote:
>>> 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.
>>> 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).
>> Yeah, in it's current state without real versioning on notifications I
>> think
>> just adding it with a bug is fine. If nova actually had a versioning
>> mechanism
>> and made stability guarantees on notifications it would be a different
>> story.
> I'm fine either way...just wanted to be sure the decision was made
> consciously.
> Chris
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Nice timing on the discussion here, I'd been meaning to upstream a 
devref [1] that we had internally since grizzly (so it's outdated a bit) 
that moves the event notifications out of the wiki and into the nova docs.

Comments welcome on that.  I just got it posted today though so I know 
it needs quite a bit of updating.

[1] https://review.openstack.org/#/c/171291/



Matt Riedemann

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