Add environment UUID to MAAS provider.

Add environment UUID to MAAS provider.

We need a way to uniquely identify those machines in MAAS belonging to
a Juju environment. Until now Juju's MAAS provider has assumed that
all the machines that are allocated, are allocated to the environment
that Juju is working with. This is obviously wrong, and can be
disastrous.

This is the first part of work on the MAAS provider to use a unique
identifier for an environment. MAAS will record this identifier
(called 'agent_name' in MAAS) and allow its use for filtering.
This branch merely adds the UUID to the environment's config.

https://code.launchpad.net/~allenap/juju-core/maas-environment-uuid/+merge/191146

(do not edit description out of merge proposal)

[allenap, 2013-10-15 11:00:26]

Please take a look.

[rvb, 2013-10-15 11:35:00]

On 2013/10/15 11:00:26, allenap wrote:
> Please take a look.

LGTM (pretty similar to what the openstack provider does indeed)

[0]

You might want to do that in another branch, but we need a getter to fetch that
uuid or '' if it isn't set (to use '' as the agent name for already deployed
environments).

[rog, 2013-10-15 11:41:05]

LGTM - assuming environment-uuid will be added to configFields and
configDefaults
in a subsequent MP.

[allenap, 2013-10-15 12:27:01]

On 2013/10/15 11:41:05, rog wrote:
> LGTM - assuming environment-uuid will be added to configFields and
> configDefaults
> in a subsequent MP.

Thanks for pointing that out Roger.

The other fields in MAAS's configFields all have a "maas-" prefix. I'll rename
this field to have that prefix too, for consistency, and to mark it out as a
MAAS-specific fix, at least for now.

Thank you both for your reviews!

[rog, 2013-10-15 15:52:18]

On 15 October 2013 13:27,  <gavin.panella@canonical.com> wrote:
> On 2013/10/15 11:41:05, rog wrote:
>>
>> LGTM - assuming environment-uuid will be added to configFields and
>> configDefaults
>> in a subsequent MP.
>
>
> Thanks for pointing that out Roger.
>
> The other fields in MAAS's configFields all have a "maas-" prefix. I'll
> rename this field to have that prefix too, for consistency, and to mark
> it out as a MAAS-specific fix, at least for now.
>
> Thank you both for your reviews!

Might I suggest that if you do that, you change the Prepare
method to return with an error if the maas-uuid (or whatever you
decide to call it) attribute is already set? That way people
can't muck things up by setting a non-unique uuid
in their environments.yaml.

Alternatively you can leave it as environment-uuid and when
we change juju-core to generate it in Prepare for all environments,
we'll reuse that attribute and the maas code can continue to
work without further change (just a bit of code that can be
deleted at leisure).

I think I prefer the latter option, which was what I was thinking
when I LGTM'd.