While this is manifesting itself in Nova, I'm fairly certain the root cause is in Neutron/OVN. Nova waits for Neutron to tell it that the vif has been plugged by sending a so called "external event". It's basically Neutron making a POST request to the Nova API telling it "I've plugged this port." In this case, Nova never receives those events, and fails the VM creation.

Artome, but why nova is timing out after 300 seconds though we increased it to to 1200 (i.e  vif_plugging_timeout=1200)?

(In reply to anil venkata from comment #2)
> Artome, but why nova is timing out after 300 seconds though we increased it
> to to 1200 (i.e  vif_plugging_timeout=1200)?

Where did you make this change? This should normally be done on the computes, and nova_compute has to be restarted after the change for it to take effect.

yes, we have added in the compute and restarted nova_compute

(In reply to anil venkata from comment #4)
> yes, we have added in the compute and restarted nova_compute

I'm not sure what to tell you. I've tried searching through the logs for any mention of vif_plugging_timeout, but without success. Any Nova service should log its configuration when it starts, so the fact that I couldn't find it logged anywhere would indicate that perhaps it wasn't restarted?

To be explicit, the option is in the [DEFAULT] section in nova.conf that's shared between the nova_libvirt and nova_compute containers. So to set it, you need to edit the file that's somewhere in /var/lib/puppet-generated for the nova_libvirt containers (apologies for not providing the exact path, I don't have a 16.1 environment handy to double check).

I hope that helps a bit.