[2.0] Cannot connect to UI if rack controller cannot be contacted

[Mike Pontillo]

When I try to connect to the MAAS UI while the rack controller is down, I receive an RPC error because the region cannot populate the available power types.

I believe this is a regression from 1.9. Users must be able to use the UI while the rack controller is down. (this is also needed for HA, so that the user can specify a failover to a secondary rack.)

The traceback[1] here might be easier to read:

https://paste.ubuntu.com/15136979/

[1]:
2016-02-20 00:35:18 [-] Error on request (27) general.power_types: Unable to get RPC connection for rack controller 'example' (4y3h7n)
 Traceback (most recent call last):
   File "/usr/lib/python3.5/threading.py", line 862, in run
     self._target(*self._args, **self._kwargs)
   File "/opt/src/maas/networking-ui/src/provisioningserver/utils/twisted.py", line 794, in worker
     return target()
   File "/usr/lib/python3/dist-packages/twisted/_threads/_threadworker.py", line 46, in work
     task()
   File "/usr/lib/python3/dist-packages/twisted/_threads/_team.py", line 190, in doWork
     task()
 --- <exception caught here> ---
   File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 246, in inContext
     result = inContext.theWork()
   File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 262, in <lambda>
     inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
   File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 118, in callWithContext
     return self.currentContext().callWithContext(ctx, func, *args, **kw)
   File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 81, in callWithContext
     return func(*args,**kw)
   File "/opt/src/maas/networking-ui/src/maasserver/utils/orm.py", line 448, in call_within_transaction
     return func_outside_txn(*args, **kwargs)
   File "/opt/src/maas/networking-ui/src/maasserver/utils/orm.py", line 275, in retrier
     return func(*args, **kwargs)
   File "/usr/lib/python3.5/contextlib.py", line 30, in inner
     return func(*args, **kwds)
   File "/opt/src/maas/networking-ui/src/maasserver/websockets/handlers/general.py", line 170, in power_types
     return get_power_types()
   File "/opt/src/maas/networking-ui/src/maasserver/clusterrpc/power_parameters.py", line 171, in get_power_types
     power_types = get_all_power_types_from_clusters(controllers, ignore_errors)
   File "/opt/src/maas/networking-ui/src/maasserver/clusterrpc/power_parameters.py", line 187, in get_all_power_types_from_clusters
     for response in responses:
   File "/opt/src/maas/networking-ui/src/maasserver/clusterrpc/utils.py", line 51, in call_clusters
     controller.hostname, controller.system_id))
 maasserver.exceptions.ClusterUnavailable: Unable to get RPC connection for rack controller 'example' (4y3h7n)

[Blake Rouse (blake-rouse)]

This has already been fixed in latest trunk. Please be sure to be on the latest trunk before filling a bug.