[openstack-dev] [nova] Networks are not cleaned up in build failure

Murray, Paul (HP Cloud) pmurray at hp.com
Wed Jan 14 17:57:24 UTC 2015

Hi All,

I recently experienced failures getting images from Glance while spawning instances. This step comes after building the networks in the guild sequence. When the Glance failure occurred the instance was cleaned up and rescheduled as expected, but the networks were not cleaned up. On investigation I found that the cleanup code for the networks is in the compute manager's _do_build_run_instance() method as follows:

            # NOTE(comstud): Deallocate networks if the driver wants
            # us to do so.
            if self.driver.deallocate_networks_on_reschedule(instance):
                self._cleanup_allocated_networks(context, instance,

The default behavior in for the deallocate_networks_on_schedule() method defined in ComputeDriver is:

    def deallocate_networks_on_reschedule(self, instance):
        """Does the driver want networks deallocated on reschedule?"""
        return False

Only the Ironic driver over rides this method to return True, so I think this means the networks will not be cleaned up for any other virt driver.

Is this really the desired behavior?

I have filed a bug for this and plan to fix it: https://bugs.launchpad.net/nova/+bug/1410739

My initial thought is to fix this either by making the method in the base class return True or by adding the method to virt drivers returning True (I would expect the former). But I wanted to check if there is a reason for the base class behavior (and so the default behavior) to be *NOT* to clean up the networks?


Paul Murray
Nova Technical Lead, HP Cloud
+44 117 316 2527

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