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On 04/23/2018 05:51 PM, Arvind N wrote:
> Thanks for the detailed options Matt/eric/jay.
> 
> Just few of my thoughts,
> 
> For #1, we can make the explanation very clear that we rejected the 
> request because the original traits specified in the original image and 
> the new traits specified in the new image do not match and hence rebuild 
> is not supported.

I believe I had suggested that on the spec amendment patch. Matt had 
concerns about an error message being a poor user experience (I don't 
necessarily disagree with that) and I had suggested a clearer error 
message to try and make that user experience slightly less sucky.

> For #3,
> 
> Even though it handles the nested provider, there is a potential issue.
> 
> Lets say a host with two SRIOV nic. One is normal SRIOV nic(VF1), 
> another one with some kind of offload feature(VF2).(Described by alex)
> 
> Initial instance launch happens with VF:1 allocated, rebuild launches 
> with modified request with traits=HW_NIC_OFFLOAD_X, so basically we want 
> the instance to be allocated VF2.
> 
> But the original allocation happens against VF1 and since in rebuild the 
> original allocations are not changed, we have wrong allocations.

Yep, that is certainly an issue. The only solution to this that I can 
see would be to have the conductor ask the compute node to do the 
pre-flight check. The compute node already has the entire tree of 
providers, their inventories and traits, along with information about 
providers that share resources with the compute node. It has this 
information in the ProviderTree object in the reportclient that is 
contained in the compute node resource tracker.

The pre-flight check, if run on the compute node, would be able to grab 
the allocation records for the instance and determine if the required 
traits for the new image are present on the actual resource providers 
allocated against for the instance (and not including any child 
providers not allocated against).

Or... we chalk this up as a "too bad" situation and just either go with 
option #1 or simply don't care about it.

Best,
-jay