Apex domains cannot have CNAME records.
Question and response
Question
dig s3-r-w.eu-central-1.amazonaws.com. NS
Answer
s3-r-w.eu-central-1.amazonaws.com. 5 NS ns-458.awsdns-57.com.
s3-r-w.eu-central-1.amazonaws.com. 5 NS ns-1065.awsdns-05.org.
s3-r-w.eu-central-1.amazonaws.com. 5 NS ns-805.awsdns-36.net.
s3-r-w.eu-central-1.amazonaws.com. 5 NS ns-1782.awsdns-30.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0