I think the port should not be deleted when the interface is detched,if the port is created independently.

I would also post this in the quantum quantum section.

I view the codes.

In the method nova.compute.manager.ComputeManager.detach_interface(),the method nova.network.quantumv2.api.API.deallocate_port_for_instance() is called where the port is deleted.

def deallocate_port_for_instance(self, context, instance, port_id,
                                     conductor_api=None):
        try:
            quantumv2.get_client(context).delete_port(port_id)
        except Exception as ex:
            LOG.exception(_("Failed to delete quantum port %(port_id)s ") %
                          locals())

This may be the problem.

Currently there is no distinction between a port created explicitly by a user or admin and a port created by the infrastructure (in this case Nova), so all ports are equal and disposed of when the resource that is using it is destroyed (in this case a VM).

I think it is fair to create a bug report and mark the bug as wishlist or opinion to see what people think about this particular issue.

I believe the bug reports above are somewhat related to the issue we are seeing here, i.e. the port gets deleted when the VM is destroyed.

They just help provide a little more context.