Unit assignment to "unused" machines

Nick Barcet nick.barcet at canonical.com
Sun Dec 25 10:44:00 UTC 2011

On 12/25/2011 10:22 AM, William Reade wrote:
> In light of the above, it seems to me that we should temporarily back
> out the use of assign_to_unused_machine, and *always* create new
> machines for new units; this means we won't get to reuse machines, ofc
> [0], but we also won't risk weird and hard-to-repro bugs caused by
> not-actually-stopped units sharing machines.
> I should reiterate that I don't oppose the feature, and I would be glad
> to see it reinstated when it's safe to do so; but it's *currently* doing
> more harm than good, and that's justification enough to cut it for now.

One thing that we might miss when removing this assign_to_unused_machine
is the ability to "prestart machines" so that they are readily available
when we really need them.  Starting a machine takes time, specially on
bare metal, but anywhere else too, and I think we have been using this
"trick" to speed up demos.  A null charm was used to fire up "empty"
machines to that objective.

Maybe we need to have a pre-provisioning option in 'juju deploy' to
allow for this behavior in a more sensible manner. For example:
$juju deploy --preprovision <myservice> 5
would do everything to start 5 machines, up to the install hook
(including it), but wait until a 'juju add-unit <myservice>' is called
to actually continue with other events?

This would also be useful for highly busy system that need to respond
quickly to change in their loads...


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