[Maas-devel] RFC: "Serialising" power actions
Julian Edwards
julian.edwards at canonical.com
Tue Oct 7 00:44:07 UTC 2014
On Tuesday 23 Sep 2014 11:00:39 Mark Shuttleworth wrote:
> > Here's my counter proposal again, which I think is a lot simpler:
> > 1 Already implemented: pserv is dumb and just issues power commands as
> >
> > requested, with a callback to the region for failure and success.
>
> The main process needs to be able to:
>
> * know that something has timed out
> * stop it from continuing
> * verify that the BMC is not "stuck" in some way, before
> * declaring the previous effort a failure and either retrying or giving
> up with an error
>
> I worry, if pserv is a "dumb fire and forget" mechanism, that this will
> be hard. We will once again be throwing a job over the fence and hoping
> we get a callback. Stay in control.
>
> > 2 We do not allow concurrent power operations while an outstanding one is
> >in >
> > progress (ie wait for the callback), although you could detect a request
> > that is the same as the outstanding one and respond without an error.
>
> Agreed, BUT you can't just wait for callback, you HAVE to be able to
> decide time's up and resume control without having a rogue process out
> there still trying to do something. Control means you STOP whatever was
> being attempted, you reassert and verify your ability to talk to the
> BMC, then you either retry or give up on that effort.
I was a little inaccurate with my use of "dumb".
In reality, pserv has some smarts and attempts retries, and will eventually
time out if the action is failing.
The upshot is that MAAS is indeed in full control at all times; we are no
longer in the bad old days of fire and forget.
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