Need to add 10,000+ DNS records.

I manage the DNS server for my own domains. Until now, the records have been your normal kind; sub domains, CNames, mail servers etc. Now I am offering a SaaS solution where people can point their own domain to it. For example:

• MySaaS.TheirDomain.com.

However, until they edit their own DNS to add that sub domain, I need to offer access via my domain. For example:

• ClientID.SaaSDomain.com

I already have the Nginx proxy set to handle and route ANY subdomain to the right server. When they sign up, their ClientID is stored in the DB, and the web server knows what to do.

However, I will need to either automate editing the DNS records each time (bad idea), or add something like 10,000 pre-defined subdomains in the DNS (another bad idea), or figure out how to have the DNS handle a 'variable' subdomain.

I have never heard of the 'variable' sub domain option, but there must be functionality something like that.

Can someone point me in the right direction?

Thanks!