I'm so sorry because this question doesn't related to Ubuntu. I asked in Openstack forum but this forum is not very active. So I think if someone have experience with Openstack Nova can help me with my problem.

I've read some explanations about nova-network and how to configure it like this one from wiki: http://wiki.openstack.org/UnderstandingFlatNetworking

I'm confusing about a detail. If every traffic from the instances must go through nova controller node, then why we still need the public interface for nova-compute node? Is it necessary?

What happen when a request from outside to an instance. For example I have a controller node and a nova-compute node. In nova-compute node I run an instance with a Wordpress website. Then someone connect to the public IP of this instance. So the request go directly from router to the nova-compute node or from router to controller node then nova-compute node?

Thank you!