Apex domains cannot have CNAME records.
Question and response
Question
dig ap-southeast-2.elb.amazonaws.com. NS
Answer
ap-southeast-2.elb.amazonaws.com. 5 NS ns-99.awsdns-12.com.
ap-southeast-2.elb.amazonaws.com. 5 NS ns-1910.awsdns-46.co.uk.
ap-southeast-2.elb.amazonaws.com. 5 NS ns-1456.awsdns-54.org.
ap-southeast-2.elb.amazonaws.com. 5 NS ns-654.awsdns-17.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0