[ovirt-devel] Reference implementation of events

[Lior Vernia]

On 09/02/15 17:23, Piotr Kliczewski wrote:
> Hi,
> 
> As you may know I currently work on event infrastructure which will
> let vdsm push information to the engine. I already pushed some drafts
> providing event functionality and started to think which part of
> engine <-> vdsm interaction could be changed to events. The goal is to
> build usable api for it as well as provide example how to migrate
> other parts of code to events.
> 
> Initially we started to look at VM.getStats [1] but we still want to
> have Host.getAllVmStats run by quartz job. I had a chat with Vinzenz
> about the structure and frequency of data change for VM.getStats and
> it seems that the data changes ~2s so this verb is not the best choice
> to send events with deltas containing the change since we are polling
> every 3s for the information.
> 
> We started to explore which data generated by vdsm/guest agent could
> be sent as events and he pointed me to [2].
> 
> I would like to trigger discussion about how to dived data to maximize
> benefits of sending events with deltas and for some parts of data keep
> polling functionality as it is now.
> 
> Do you have any suggestion which verb we could safely use as reference
> implementation for events?

I'm not sure what you mean by "safely", but a good candidate (in terms
of both low frequency of changes and value of triggered events) would be
getVdsCaps. Especially if only deltas are sent.

For example, we'd love get relevant data from vdsm whenever a network
interface's IP address changes (an event which phoracek is currently
working on monitoring).

That's one example I know from networking, but maybe such examples exist
where the monitoring is already implemented and ready to be tested via
event triggering.

> 
> Thanks,
> Piotr
> 
> [1] http://gerrit.ovirt.org/#/c/37488/
> [2] http://www.ovirt.org/Proposal_VDSM_-_Engine_Data_Statistics_Retrieval
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