Apex domains cannot have CNAME records.
Question and response
Question
dig ap-northeast-1.amazonaws.com. NS
Answer
ap-northeast-1.amazonaws.com. 5 NS ns-1007.awsdns-61.net.
ap-northeast-1.amazonaws.com. 5 NS ns-1419.awsdns-49.org.
ap-northeast-1.amazonaws.com. 5 NS ns-1941.awsdns-50.co.uk.
ap-northeast-1.amazonaws.com. 5 NS ns-68.awsdns-08.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0