What is a good DNS service under SAAS?

Question

Domain Name System

We are developing a SAAS service, it is necessary to enable users to connect their domains by registering our NS (we assume that a large number of registrars do not provide DNS for free at all, without ordering hosting from them).
The most obvious option is to raise your DNS, write the simplest API (or without bicycles?) and implement this functionality. But attacks through DNS server DDos are very very popular now - in connection with this, we are looking for a service for organizing DNS, for adequate money. We plan to make the monthly tariff for each client quite low, so we are looking for a budgetary, but adequate solution.
99% of customers will connect their domains.

Answer 1

And why not implement it through the usual host mapping, that is, for clients to simply create a CNAME record for their domain, which will point to your standard domain?
In the West, almost all services do this. For example, the same Tumblr. Very simple and convenient solution.

Answer 2

Try dyn.com