Comment 3 for bug 1205451

From @Dave's other duplicate:

Scenario:

Customer has used juju add-machine to enroll all their maas nodes * into their juju environment.

During this process one or more of the machines crashed, but a machine record exists for it, so it appears as 'unallocated' in juju status.

That dead machine will attract units made with add-unit / deploy yet never be able to provision them, nor can units that land on these zombie machines be removed, see lp#1206532.

Proposal:

Juju should consider the agent presence status at the point in time it tries to find a free machine to allocate the unit too. Machines which are currently failing presence would be excluded.

* in the exact scenario, this was so they could use add-unit --to to work around the lack of maas tags, but the underlying problem is applicable without this fact.