Apex domains cannot have CNAME records.
Question and response
Question
dig ap-northeast-1.elb.amazonaws.com. NS
Answer
ap-northeast-1.elb.amazonaws.com. 4 NS ns-1325.awsdns-37.org.
ap-northeast-1.elb.amazonaws.com. 4 NS ns-982.awsdns-58.net.
ap-northeast-1.elb.amazonaws.com. 4 NS ns-54.awsdns-06.com.
ap-northeast-1.elb.amazonaws.com. 4 NS ns-1683.awsdns-18.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0