[openstack-dev] [Nova] State machines in Nova
mgould at redhat.com
Wed Jun 1 09:51:09 UTC 2016
On 31/05/16 21:03, Timofei Durakov wrote:
> there is blueprint that was approved during Liberty and resubmitted
> to Newton(with spec).
> 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.
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