adding Juju nodes from MAAS _manually_

[Peter Grandi]

> Potentially given that we rather rarely add or remove physical
> servers from our small (12 nodes) the cluster arguably we
> don't really need MAAS,

Actually it turns out that the MAAS upgrade issue we had was
fixable, and I have gained some more appreciation of MAAS as its
RDMBS based state store seems moderately sensible and it has
turned out to be eays to fix manually when it gets in some less
than consistent state.

> In theory one static node provider is the same to Juju as
> another, would it be possible to "transparently" convert our
> Juju nodes from MAAS-provided nodes to manually managed nodes?

Looking at:

  https://jujucharms.com/docs/stable/config-manual

    «It is possible to manually provision machines into non-manual
    provider environments, however the machine must be placed on the
    same private subnet as the other machines in the environment.»

It seems that *extending* an existing Juju setup with manually
provisioned systems is already supported (with the qualification
above), which might be good enough, while continuining to use
MAAS. Converting existing auto-provisioned "machines" to manual
probably would require hand-editing of the MongoDB state
database instead.

It would be nice to see some confirmation that acquiring a MAAS
"node" as 'root' and then manually adding it to our existing
Juju setup as a new "machine" ought to work.

We are also considering creating two distinct Juju environments,
the existing one for automatically provisioned systems, and a
new one for manually provisioned ones, but since we would like
to run the same OpenStack and Ceph clusters across both I
suspect it would be (far) easier to just have all relevant
"machines" in the existing Juju "environment".

The reason BTW why we are considering this is that we are not
too confident in Juju's acquiring "machines" reliabily, and
anyhow out small hardware collection is better managed manually
as we don't want Juju to grab a random available "node" from
MAAS but usually a specific one, for various reasons, and then
it is just simpler to hand it to Juju manually.