Comment 1 for bug 1560971

Same issue on Ubuntu Mate 16.04 ARMHF (Raspberry Pi 3B):

VERSIONS
root@juju-rack2:~# cat /etc/issue
Ubuntu 16.04.1 LTS \n \l

root@juju-rack2:~# uname -a
Linux juju-rack2.home.spyderdyne.net 4.4.43-v7+ #948 SMP Sun Jan 15 22:20:07 GMT 2017 armv7l armv7l armv7l GNU/Linux

MAAS Version 2.1.3+bzr5573-0ubuntu1 (16.04.1) - From PPA stable...

Unfortunately, dpkg-reconfigure doesn't fix the issue. I manually added the API key back to try to correct following the instructions here:

https://maas.ubuntu.com/docs/rack-configuration.html#registration

running "dpkg-reconfigure maas-rack-controller" per the instructions provided.

Still not connected. Checking the log at /var/log/maas/rackd.log I see it was unable to connect to itself at 127.0.0.1 and finally shut itself down:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 588, in _runCallbacks
    current.result = callback(current.result, *args, **kw)
  File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1184, in gotResult
    _inlineCallbacks(r, g, deferred)
  File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1126, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
--- <exception caught here> ---
  File "/usr/lib/python3/dist-packages/provisioningserver/rpc/clusterservice.py", line 978, in update
    info = yield self._fetch_rpc_info(info_url)
twisted.web.error.Error: 500 INTERNAL SERVER ERROR
2017-01-19 12:15:59 -: [info] Received SIGTERM, shutting down.
2017-01-19 12:17:20 -: [info] twistd 16.0.0 (/usr/bin/python3 3.5.2) starting up.
2017-01-19 12:17:20 -: [info] reactor class: twisted.internet.epollreactor.EPollReactor.

Rebooting show the config updated successfully, but the region controller is refusing the rack controller now:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 588, in _runCallbacks
    current.result = callback(current.result, *args, **kw)
  File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1184, in gotResult
    _inlineCallbacks(r, g, deferred)
  File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1126, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
--- <exception caught here> ---
  File "/usr/lib/python3/dist-packages/provisioningserver/rpc/clusterservice.py", line 978, in update
    info = yield self._fetch_rpc_info(info_url)
twisted.web.error.Error: 500 INTERNAL SERVER ERROR
2017-01-19 12:15:59 -: [info] Received SIGTERM, shutting down.
2017-01-19 12:17:20 -: [info] twistd 16.0.0 (/usr/bin/python3 3.5.2) starting up.
2017-01-19 12:17:20 -: [info] reactor class: twisted.internet.epollreactor.EPollReactor.

Still digging...