[openstack-dev] [Nova] State machines in Nova

Joshua Harlow harlowja at fastmail.com
Wed Jun 1 15:45:52 UTC 2016

Miles Gould wrote:
> On 31/05/16 21:03, Timofei Durakov wrote:
>> there is blueprint[1] that was approved during Liberty and resubmitted
>> to Newton(with spec[2]).
>> The idea is to define state machines for operations as live-migration,
>> resize, etc. and to deal with them operation states.
> +1 to introducing an explicit state machine - IME they make complex
> logic much easier to reason about. However, think carefully about how
> you'll make changes to that state machine later. In Ironic, this is an
> ongoing problem: every time we change the state machine, we have to
> decide whether to lie to older clients (and if so, what lie to tell
> them), or whether to present them with the truth (and if so, how badly
> they'll break). AIUI this would be a much smaller problem if we'd
> considered this possibility carefully at the beginning.

Do u have any more details (perhaps an 'real-life' example that you can 
walk us through) of this and how it played out. It'd be interesting to 
hear (I believe it has happened a few times but I've never heard how it 
was resolved or the details of it).

> Miles
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