Apex domains cannot have CNAME records.
Question and response
Question
dig r-rooter.com. NS
Answer
r-rooter.com. 5 NS ns-1497.awsdns-59.org.
r-rooter.com. 5 NS ns-411.awsdns-51.com.
r-rooter.com. 5 NS ns-443.awsdns-55.com.
r-rooter.com. 5 NS ns-452.awsdns-56.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0