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On 11/09/15 12:19, Sean Dague wrote:
> On 09/11/2015 05:41 AM, Matthew Booth wrote:
>> I've recently been writing a tool which uses Nova's external API. This
>> is my first time consuming this API, so it has involved a certain amount
>> of discovery. The tool is here for the curious:
>>
>>   https://gist.github.com/mdbooth/163f5fdf47ab45d7addd
>>
>> I have felt hamstrung by the general inability to distinguish between
>> different types of error. For example, if a live migration failed is it
>> because:
>>
>> 1. The compute driver doesn't support support it.
>>
>> 2. This instance requires block storage migration.
>>
>> 3. Something ephemeral.
>>
>> These 3 errors all require different responses:
>>
>> 1. Quit and don't try again.
>>
>> 2. Try again immediately with the block migration argument.[1]
>>
>> 3. Try again in a bit.
>>
>> However, all I have is that I made a BadRequest. I could potentially
>> grep the human readable error message, but the text of that message
>> doesn't form part of the API, and it may be translated in any case. As
>> an API consumer, it seems I can't really tell anything other than 'it
>> didn't work'. More than that requires guesswork, heuristics and inference.
>>
>> I don't think I've missed some source of additional wisdom, but it would
>> obviously be great if I have. Has there ever been any effort to define
>> some contract around more fine-grained error reporting?
>>
>> Thanks,
>>
>> Matt
>>
>> [1] Incidentally, this suggests to me that live migrate should just do
>> this anyway.
> 
> This is an API working group recommendation evolving here. The crux of
> which is going to be a structured json error return document that will
> contain more info. https://review.openstack.org/#/c/167793/

Thanks, Sean, that's exactly what I was looking for. I'll continue this
discussion in that review.

Matt
-- 
Matthew Booth
Red Hat Engineering, Virtualisation Team

Phone: +442070094448 (UK)
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