Comment 1 for bug 527648

That analysis tends to be confirmed by my latest test:

From the CC+SC, I can ping and try to connect by ssh to the karmic instance.
SSH connection fails because of publickey, which tends to prove the instance could not query the metadata service to get it.

So it seems like the instance cannot contact the CLC+Walrus (to query metadata) and that the CLC+Walrus cannot contact the public/private address of the instance (for ping or SSH).