Apex domains cannot have CNAME records.
Question and response
Question
dig ap-southeast-1.compute.amazonaws.com. NS
Answer
ap-southeast-1.compute.amazonaws.com. 5 NS ns-1460.awsdns-54.org.
ap-southeast-1.compute.amazonaws.com. 5 NS ns-65.awsdns-08.com.
ap-southeast-1.compute.amazonaws.com. 5 NS ns-914.awsdns-50.net.
ap-southeast-1.compute.amazonaws.com. 5 NS ns-1886.awsdns-43.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0