VPN from my server to a clients
Solution 1:
Check this out, what you really want to do, is get a router / VPN config in Amazon that can act as a central point for VPN connecions Just be mindful of security.
http://aws.amazon.com/vpc/
Solution 2:
Check out tinc: http://tinc-vpn.org/ It is a fairly robust alternative to classic VPN implementations: It doesn't need a star-like client/server setup. Every node can be set up to try to establish a VPN connection to the other node(s) on its own but it really only needs one of these attempts to succeed for the tunnel to work.