Apex domains cannot have CNAME records.
Question and response
Question
dig scalabledns.com. NS
Answer
scalabledns.com. 4 NS ns1.scalabledns.com.
scalabledns.com. 4 NS ns2.scalabledns.com.
Authority
The response has no authority records.
Additional
ns1.scalabledns.com. 4 A 194.124.244.10
ns2.scalabledns.com. 4 A 38.145.192.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0