Apex domains cannot have CNAME records.
Question and response
Question
dig s3-r-w.eu-west-1.amazonaws.com. NS
Answer
s3-r-w.eu-west-1.amazonaws.com. 5 NS ns-1228.awsdns-25.org.
s3-r-w.eu-west-1.amazonaws.com. 5 NS ns-56.awsdns-07.com.
s3-r-w.eu-west-1.amazonaws.com. 5 NS ns-777.awsdns-33.net.
s3-r-w.eu-west-1.amazonaws.com. 5 NS ns-1961.awsdns-53.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0