Apex domains cannot have CNAME records.
Question and response
Question
dig s3-w.eu-central-1.amazonaws.com. NS
Answer
s3-w.eu-central-1.amazonaws.com. 5 NS ns-531.awsdns-02.net.
s3-w.eu-central-1.amazonaws.com. 5 NS ns-1346.awsdns-40.org.
s3-w.eu-central-1.amazonaws.com. 5 NS ns-1759.awsdns-27.co.uk.
s3-w.eu-central-1.amazonaws.com. 5 NS ns-455.awsdns-56.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0