file synchronization solutions

I have two servers connected via Internet (NOT IN THE SAME LAN) serving the same website ( problem is files uploaded on serverA and serverB cannot see each other immediately,thus rsync with certain intervals is not a good solution.
Can anybody give me some advice on the following options?

1.NFS over Internet for file sharing
3.inotify(our system's kernel does not support this and we donot want to risk upgrading our kernel as well)
4.drbd in active-active mode
5 or any other solutions

Any suggestions will be welcomed.
Thank you in advance.