Today when I used Openstack, I made a mistake. Because of some debug issues I created a Ubuntu image while changing its /etc/network/interfaces to static IP[1], which makes the OpenStack can't not assign the internal IP and Floating IP to the instances
created by this image. I couldn't ping any of these instances because of this issue. It took me quite a while to figure it out since I was wondering is there any thing went wrong with the OpenStack again.
As for the floating ip operations such as associate, disassociate, create and delete, we can use the quantum commands[2] directly, or dashboard. The '+' symbol in the picture means creating a new floating ip, like the command "quantum floatingip-create
<ext network id>"[2].
Reference:
[1]https://help.ubuntu.com/community/NetworkConfigurationCommandLine/Automatic
[2] http://docs.openstack.org/grizzly/openstack-network/admin/content/l3_workflow.html