Comment 6 for bug 2068727

I spent some time with this issue, and I am far from understanding the background of it.
What is visible that Nova waits for the the vif-plugged event but never receives it :

Jul 20 09:01:52.344791 np0038023667 nova-compute[67176]: WARNING nova.compute.manager [None req-3db28b46-1d8a-4493-857b-d8d6d20960a6 tempest-TestSfc-1936475685 tempest-TestSfc-1936475685-project-member] [instance: 172f4314-32b0-4c86-a893-b70168117c41] Timeout waiting for ['network-vif-plugged-c0dcf72b-bae7-467a-923e-8e9523200eb3'] for instance with vm_state building and task_state spawning. Event states are: network-vif-plugged-c0dcf72b-bae7-467a-923e-8e9523200eb3: timed out after 300.00 seconds: eventlet.timeout.Timeout: 300 seconds

The strange thing is that all this happens before any sfc operation is done:
https://opendev.org/openstack/neutron-tempest-plugin/src/branch/master/neutron_tempest_plugin/sfc/tests/scenario/test_sfc.py#L103-L105