nova/releasenotes/notes/bug-1946729-wait-for-vif-plugged-event-during-hard-reboot-fb491f6a68370bab.yaml
Balazs Gibizer 68c970ea99 Add a WA flag waiting for vif-plugged event during reboot
The libvirt driver power on and hard reboot destroys the domain first
and unplugs the vifs then recreate the domain and replug the vifs.
However nova does not wait for the network-vif-plugged event before
unpause the domain. This can cause that the domain starts running and
requesting IP via DHCP before the networking backend finished plugging
the vifs.

So this patch adds a workaround config option to nova to wait for
network-vif-plugged events during hard reboot the same way as nova waits
for this event during new instance spawn.

This logic cannot be enabled unconditionally as not all neutron
networking backend sending plug time events to wait for. Also the logic
needs to be vnic_type dependent as ml2/ovs and the in tree sriov backend
often deployed together on the same compute. While ml2/ovs sends plug
time event the sriov backend does not send it reliably. So the
configuration is not just a boolean flag but a list of vnic_types
instead. This way the waiting for the plug time event for a vif that is
handled by ml2/ovs is possible while the instance has other vifs handled
by the sriov backend where no event can be expected.

Change-Id: Ie904d1513b5cf76d6d5f6877545e8eb378dd5499
Closes-Bug: #1946729
2021-11-04 16:09:12 +01:00

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YAML

---
issues:
- |
The libvirt virt driver in Nova implements power on and hard reboot by
destroying the domain first and unpluging the vifs then recreating the
domain and replugging the vifs. However nova does not wait for the
network-vif-plugged event before unpause the domain. This can cause
the domain to start running and requesting IP via DHCP before the
networking backend has finished plugging the vifs. The config option
[workarounds]wait_for_vif_plugged_event_during_hard_reboot has been added,
defaulting to an empty list, that can be used to ensure that the libvirt
driver waits for the network-vif-plugged event for vifs with specific
``vnic_type`` before it unpauses the domain during hard reboot. This should
only be used if the deployment uses a networking backend that sends such
event for the given ``vif_type`` at vif plug time. The ml2/ovs and the
networking-odl Neutron backend is known to send plug time events for ports
with ``normal`` ``vnic_type``. For more information see
https://bugs.launchpad.net/nova/+bug/1946729