Apex domains cannot have CNAME records.
Question and response
Question
dig s3.us-east-1.amazonaws.com. NS
Answer
s3.us-east-1.amazonaws.com. 5 NS ns-193.awsdns-24.com.
s3.us-east-1.amazonaws.com. 5 NS ns-1184.awsdns-20.org.
s3.us-east-1.amazonaws.com. 5 NS ns-689.awsdns-22.net.
s3.us-east-1.amazonaws.com. 5 NS ns-2021.awsdns-60.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0