Apex domains cannot have CNAME records.
Question and response
Question
dig amazonaws.com. NS
Answer
amazonaws.com. 4 NS ns-1670.awsdns-16.co.uk.
amazonaws.com. 4 NS ns-1321.awsdns-37.org.
amazonaws.com. 4 NS ns-27.awsdns-03.com.
amazonaws.com. 4 NS ns-967.awsdns-56.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0