Apex domains cannot have CNAME records.
Question and response
Question
dig s3-us-west-2.amazonaws.com. NS
Answer
s3-us-west-2.amazonaws.com. 5 NS ns-1256.awsdns-29.org.
s3-us-west-2.amazonaws.com. 5 NS ns-656.awsdns-18.net.
s3-us-west-2.amazonaws.com. 5 NS ns-307.awsdns-38.com.
s3-us-west-2.amazonaws.com. 5 NS ns-1664.awsdns-16.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0