Apex domains cannot have CNAME records.
Question and response
Question
dig as15108.com. NS
Answer
as15108.com. 5 NS ns-1557.awsdns-02.co.uk.
as15108.com. 5 NS ns-521.awsdns-01.net.
as15108.com. 5 NS ns-4.awsdns-00.com.
as15108.com. 5 NS ns-1111.awsdns-10.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0