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

Timofei Durakov tdurakov at mirantis.com
Tue May 31 20:03:45 UTC 2016

Hi team,

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.
The spec PoC patches are overall good. At the same time I think is will be
good to get agreement on the usage of state-machines in Nova.
There are 2 options:

   - implement proposed change and use state machines to deal with states
   - procs:
         - could be implemented/merged right now
         - cleans up states for migrations
      - cons:
         - state machine only deal with states, and it will be hard to
         build on top of it task API, as bp [1] was designed for another thing.

   - use state machines in Task API(which I'm going to work on during next
      - procs:
         - Task API will orchestrate and deal with long running tasks
         - usage state-machines could help with actions
      - cons:
         - big amount of work
         - requires time.

I'd like to discuss these options in this thread.


[1] -
[2] - https://review.openstack.org/#/c/320849/
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