Apex domains cannot have CNAME records.
Question and response
Question
dig s3-website.sa-east-1.amazonaws.com. NS
Answer
s3-website.sa-east-1.amazonaws.com. 5 NS ns-1211.awsdns-23.org.
s3-website.sa-east-1.amazonaws.com. 5 NS ns-298.awsdns-37.com.
s3-website.sa-east-1.amazonaws.com. 5 NS ns-565.awsdns-06.net.
s3-website.sa-east-1.amazonaws.com. 5 NS ns-1943.awsdns-50.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0