Apex domains cannot have CNAME records.
Question and response
Question
dig s3-website.eu-central-1.amazonaws.com. NS
Answer
s3-website.eu-central-1.amazonaws.com. 5 NS ns-1190.awsdns-20.org.
s3-website.eu-central-1.amazonaws.com. 5 NS ns-1890.awsdns-44.co.uk.
s3-website.eu-central-1.amazonaws.com. 5 NS ns-478.awsdns-59.com.
s3-website.eu-central-1.amazonaws.com. 5 NS ns-635.awsdns-15.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0