Apex domains cannot have CNAME records.
Question and response
Question
dig s3-eu-west-1-r-w.amazonaws.com. NS
Answer
s3-eu-west-1-r-w.amazonaws.com. 5 NS ns-206.awsdns-25.com.
s3-eu-west-1-r-w.amazonaws.com. 5 NS ns-1447.awsdns-52.org.
s3-eu-west-1-r-w.amazonaws.com. 5 NS ns-798.awsdns-35.net.
s3-eu-west-1-r-w.amazonaws.com. 5 NS ns-1645.awsdns-13.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0