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-552.awsdns-05.net.
s3-website-sa-east-1.amazonaws.com. 5 NS ns-1414.awsdns-48.org.
s3-website-sa-east-1.amazonaws.com. 5 NS ns-1893.awsdns-44.co.uk.
s3-website-sa-east-1.amazonaws.com. 5 NS ns-152.awsdns-19.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0