Machine agents uninstall themselves upon worker.ErrTerminateAgent.

[Eric Snow]

On Mon, May 9, 2016 at 1:56 AM, Andrew Wilkins
<andrew.wilkins at canonical.com> wrote:
> But... I've just looked at the 1.25 branch again, and the fix *was* made
> there. And from Jorge's comment
> https://bugs.launchpad.net/juju-core/+bug/1514874/comments/4, we can see
> that the uninstall logic isn't actually running (see `uninstall file
> "/var/lib/juju/uninstall-agent" does not exist`
> https://github.com/juju/juju/blob/1.25/cmd/jujud/agent/machine.go#L1741)
>
> I'm not sure what to make of that. Eric, have you confirmed that that code
> is what's causing the issue? Are we sure we're not barking up the wrong
> tree?

Those logs certainly don't line up with the reported bug. :/  It's
possible that they aren't the right logs.  Regardless, my initial
investigation was based on inspecting code that "uninstalls" the
agent.  The only such code I found was machineAgent.uninstallAgent()
(and in the manual provder's Destroy()).

To be sure about it, I verified the issue using the LXD provider under
2.0, following the steps Jorge specified in the bug:

1) Modify the apipassword on the /var/lib/juju/agents/machine-8/agent.conf
2) Restart jujud-machine-8

The agent is uninstalled and the the uninstall file is there:

  2016-05-09 16:21:48 INFO juju.agent uninstall.go:47 agent already
marked ready for uninstall

However, the machine is still there:

  $ juju status
  ...
  0          started 10.235.227.113
juju-af8e08f2-3953-4bcb-84de-767a15f46b4f-machine-0 xenial

I'll check it with 1.25 too, though I expect that the result will be the same.

-eric