Start with the Security Groups you've assigned to the instance. Check out what you are allowing in/out. Then move on to the instance itself, look at the iptables rules you have setup. If you want to test connectivity without setting up rules on the instance you can run: iptables -F to flush the current rules. If that's not it, make sure your services are listening on the right ports: netstat -nat, see what's listening on 21, if it's 127.0.0.1 then you need to modify your ftp configuration to listen on the right IP address or on all with listen: 0.0.0.0. If they aren't listening at all then you need to make sure the service is even running, if you started it and it's not running check the service logs for errors.