freeradius with cloud authentication

I am using freeradius server locally on ubuntu machine , and my system working fine . I want to allow my system to run from cloud to start sell it , but I don’t know how to make my freeradius working on cloud . clients don’t have public ip address , I searched alote in the internet and found many cloud Radius server , they using NAS-ID attribute , but I don’t know how freeradius and NAS can makeing connection and authentication through NAS-ID . When I running my system locally I insert NAS information into nas table, like nas ip and secret ,but that because NAS and freeradius server running at same network so they can connect together , so how can I do that ? Thank you