If you have many different remote devices behind NATs or firewalls, a cool trick to access them all via EC2 server (or such) is to setup Remote Forwarding via UNIX socket on the server side, to devices' port 22. Preferably, UNIX socket filenames should start with a common prefix, so an SSH config can be written that will use ssh+socat in a ProxyCommand to establish the connection.

It's amazing how lightweight this method actually is. I have managed to connect hundreds of devices using a single EC2 nano instance.