vm: only destroy node dependent entities when node is available

circle/vm/models/instance.py

@@ -437,7 +437,7 @@ class Instance(AclBase, VirtualMachineDescModel, TimeStampedModel):
         """Get the remote worker queue name of this instance with the specified
            queue ID.
         """
-        return self.node.get_remote_queue_name(queue_id)
+        return self.node.get_remote_queue_name(queue_id) if self.node else None
 
     def renew(self, which='both'):
         """Renew virtual machine instance leases.
@@ -535,9 +535,13 @@ class Instance(AclBase, VirtualMachineDescModel, TimeStampedModel):
                           asynchronously.
         :type task_uuid: str
         """
+        if self.destroyed:
+            return  # already destroyed, nothing to do here
+
         with instance_activity(code_suffix='destroy', instance=self,
                                task_uuid=task_uuid, user=user) as act:
 
+            if self.node:
                 # Destroy networks
                 with act.sub_activity('destroying_net'):
                     for net in self.interface_set.all():