Unit assignment to "unused" machines

[Gustavo Niemeyer]

Hey William,

> 1) No stop hooks will be fired (lp:802995; lp:872264). So, an "unused"
> machine is in fact still running the original service unit. OK, we
> should fix those bugs by 12.04; and assuming we do, we can forget about
> *this* point. But:

You're assuming something implicitly here. Assigning to an unused
machine is also done when you start several machines upfront, and then
assign to them as necessary. This scenario doesn't involve the problem
above, and needs assignment to unused machines to work.

> 2) Even if we *do* fire the stop hooks, we don't have any guarantee that
> the stop hook has *actually* shut down the service properly... AFAICT,

Same thing. You're assuming adding/removing/adding. I agree this is a
scenario we're not covering well yet, and would probably be best that
we prevented it until we do handle it well via LXC. That said,
assignment to unused continues to be useful without it.

> [0] ...but this is not an exceptionally big deal, because we will *only*
> currently reuse machines when we happen to create a new service unit in
> the window between destroying an old one and having its machine shut
> down by the PA; and that's not behaviour you can reliably induce anyway.
> Right?

Right, precisely. The reuse in this scenario, specifically, sounds
like a bug rather than intended behavior.

-- 
Gustavo Niemeyer
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-- I'm not absolutely sure of anything.