[2.5] Cannot configure DHCP on a multi-node MAAS

Restarting, saw this:

2018-09-11 21:02:19 maasserver.dhcp: [info] Successfully configured DHCPv6 on rack controller 'ycqan6'.
2018-09-11 21:02:19 maasserver.rack_controller: [critical] Failed configuring DHCP on rack controller 'id:1'.
        Traceback (most recent call last):
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1442, in gotResult
            _inlineCallbacks(r, g, deferred)
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1432, in _inlineCallbacks
            deferred.errback()
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 500, in errback
            self._startRunCallbacks(fail)
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 567, in _startRunCallbacks
            self._runCallbacks()
        --- <exception caught here> ---
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 653, in _runCallbacks
            current.result = callback(current.result, *args, **kw)
          File "/usr/lib/python3/dist-packages/maasserver/rack_controller.py", line 256, in <lambda>
            d.addErrback(lambda f: f.trap(NoConnectionsAvailable))
          File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 359, in trap
            self.raiseException()
          File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 385, in raiseException
            raise self.value.with_traceback(self.tb)
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1386, in _inlineCallbacks
            result = g.send(result)
          File "/usr/lib/python3/dist-packages/maasserver/dhcp.py", line 835, in configure_dhcp
            raise ipv4_exc
          File "/usr/lib/python3/dist-packages/maasserver/dhcp.py", line 773, in configure_dhcp
            omapi_key=config.omapi_key)
        provisioningserver.rpc.exceptions.CannotConfigureDHCP: timed out

2018-09-11 21:02:22 maasserver.dhcp: [critical] Error configuring DHCPv4 on rack controller 'ycqan6':
        Traceback (most recent call last):
        Failure: twisted.internet.defer.CancelledError:

2018-09-11 21:02:22 maasserver.dhcp: [info] Successfully configured DHCPv6 on rack controller 'ycqan6'.
2018-09-11 21:02:22 maasserver.rack_controller: [critical] Failed configuring DHCP on rack controller 'id:1'.
        Traceback (most recent call last):
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1442, in gotResult
            _inlineCallbacks(r, g, deferred)
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1432, in _inlineCallbacks
            deferred.errback()
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 500, in errback
            self._startRunCallbacks(fail)
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 567, in _startRunCallbacks
            self._runCallbacks()
        --- <exception caught here> ---
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 653, in _runCallbacks
            current.result = callback(current.result, *args, **kw)...

This is not a critical error because its not preventing MAAS from working, MAAS is handling the error and continuing to work properly.

This is the 30 second timeout that handles issues where the DHCP service gets stuck because of the service monitor.

This is a critical error. It prevents MAAS from working because DHCP is not working even when it is enabled.

Unless this is occurring constantly which would prevent DHCP from never starting, then its a critical error. But if its occurring periodically and rackd recovers from the error and fixes DHCP then its only high.