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On 1/10/2018 1:49 PM, Alec Hothan (ahothan) wrote:
> The main problem is that the nova API does not return sufficient detail 
> on the reason for a NoValidHostFound and perhaps that should be fixed at 
> that level. Extending the API to return a reason field which is a json 
> dict that is returned by the various filters  (with more meaningful 
> filter-specific info) will help tremendously (no more need to go through 
> the log to find out why).

There are security implications to doing this, which is why the ultimate 
reason behind the NoValidHost hasn't been exposed to the end user. It 
could leak details about the size, topology and configuration of the 
cloud and open it up to attacks.

A better alternative would be something like an audit log (or fault) 
that only the user with the admin role could see, like when they are 
investigating a support ticket.

There might be other cases where we should do a better job of validation 
in the API before casting off to the scheduler. If we can detect common 
reasons for a scheduling (or build) failure up front in the API, we can 
return that information immediately back to the user who can act upon 
it. That, in turn, should also improve our API documentation (assuming 
it's a common failure or something that's just not clear usage-wise in 
the docs).

-- 

Thanks,

Matt