hook for destruction

[Clint Byrum]

Excerpts from Gustavo Niemeyer's message of 2012-11-14 09:20:09 -0800:
> On Wed, Nov 14, 2012 at 3:12 PM, Clint Byrum <clint at ubuntu.com> wrote:
> > I think this succinctly spells out a reason that there is a need for
> > something beyond subordinates to define "virtual" or maybe "external"
> > services such as RDS or ELB. I opened a bug about this a long time ago:
> 
> While there's some relationship indeed, in terms of priorization it's
> important to make it clear that this is not what was asked for. The
> request is not to represent the services in a different way, but
> simply to allow for handling termination differently.
> destroy-environment would still destroy whatever else was there.

Quoting from  Marcos Barbosa to Kapil, juju  7:12am (6 hours ago)
> There's a little theory about RDS. A DB instance is  like a EC2 with MySQL.
> Inside DB instance we can create databases. I already have information
> about when the charm is deployed (install hook) to create DB instance, but
> I need know when the environment is destroyed  to delete DB instance.

I thought thats exactly what Marcos was asking for.. a way to destroy
things outside the environment, when the environment is destroyed.

If we don't have a way to make external entities first class citizens,
then yes, we have to use some kind of "destroy" hook on subordinates,
otherwise the container's destruction will result in a leaked external
resource.