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I have a couple of reviews up to introduce the concept of shelving an 
instance into Nova.  The question has been raised as to whether or not 
this belongs in Nova, or more rightly belongs in Heat.  The blueprint 
for this feature can be found at 
https://blueprints.launchpad.net/nova/+spec/shelve-instance, but to make 
things easy I'll outline some of the goals here.

The main use case that's being targeted is a user who wishes to stop an 
instance at the end of a workday and then restart it again at the start 
of their next workday, either the next day or after a weekend.  From a 
service provider standpoint the difference between shelving and stopping 
an instance is that the contract allows removing that instance from the 
hypervisor at any point so unshelving may move it to another host.

 From a user standpoint what they're looking for is:

The ability to retain the endpoint for API calls on that instance.  So 
v2/<tenant_id>/servers/<server_id> continues to work after the instance 
is unshelved.

All networking, attached volumes, admin pass, metadata, and other user 
configurable properties remain unchanged when shelved/unshelved.  Other 
properties like task/vm/power state, host, *_at, may change.

The ability to see that instance in their list of servers when shelved.



Again, the objection that has been raised is that it seems like 
orchestration and therefore would belong in Heat.  While this is 
somewhat similar to a snapshot/destroy/rebuild workflow there are 
certain properties of shelving in Nova that I can't see how to reproduce 
by handling this externally.  At least not without exposing Nova 
internals beyond a comfortable level.

So I'd like to understand what the thinking is around why this belongs 
in Heat, and how that could be accomplished.