floating ip association doesn't correctly assigned to interface specified

Fix proposed to branch: master
Review: https://review.openstack.org/17993

Folsom Fix:

interface = floating_ip['interface'] or FLAGS.public_interface

Looking to get discussion on this to see if my request makes sense.

The fix I propose seems fix the IP association but still breaks floating IPs since the public interface is still used for outbound connectivity.

Thoughts?

The code is correct. The flag is used as an override so that one can have heterogeneous nodes where the public_interface is different across nodes. For example:

Node 1:
  public_interface=eth0

Node 2:
  public_interface=eth1

If you want to use the interface from the database do not set public_interface. That is why it defaults to None.

It doesn't make sense to me that I would have to disable a flag to get something more specific to work. If I pass an interface to the floating pool, I expect that to take effect regardless of what I have set in public_interface. It's also confusing that I can specify an interface, the database will show that interface but when I assign the floating IP it doesn't apply it to the interface I want.

Removing the public_interface flag causes the default iptables SNAT rules to watch eth0 which for some installations will be an issue. Specifically, let's say eth0 is my management newtork and eth1 is my default gateway and fixed network interface, I have to have the public_interface flag set to eth1 for instances to be able to reach external networks.

The reason why this hasn't really come up before is that traffic flow and routing will be an issue if you want floating IP traffic to go out a different interface than the default gatway. Very few deployments would ever need to design something different but it does come up. This would be more common for the VLAN manager where you may want to have a floating pool for each vlan.

This may not be a huge problem since Quantum is here but it's come up for a few deployments.

I understand that it is confusing, but the current implementation is necessary to support heterogeneous nodes as I stated above. I agree that It would be less confusing if the public_interface were set to None by default. In fact, I thought this was already the case, but I see that it isn't. Unfortunately it is probably to late in the cycle to change default values so it will just have to be noted that you need to explicitly set public_interface= to use multiple floating pools.