openstack team mailing list archive

[Mark McLoughlin <markmc@xxxxxxxxxx>]

Hi Kiall,

On Sun, 2011-10-09 at 22:41 +0100, Kiall Mac Innes wrote:
> Hiya,
> 
> I'm looking to find out if there is any way to access an instance via its
> public (floating ip) from within the same instance.
> 
> The docs mention that this is not possible here:
> http://docs.openstack.org/diablo/openstack-compute/admin/content/associating-public-ip.html
> 
> My question is this: is this a physical impossibility, or a limitation of
> the current nova-network implementation?

Floating IPs are implemented by nova-network using NAT - incoming
packets in the host destined for the floating IP have their destination
changed to the fixed IP and vice versa.

i.e. from within the VM, you basically have no knowledge of your
floating IP apart by looking at e.g. the public-ipv4 property from the
EC2 metadata API or using the likes of www.whatismyip.com

It's pretty much the same situation as being behind any NAT

Cheers,
Mark.