Apex domains cannot have CNAME records.
Question and response
Question
dig s3-eu-west-1.amazonaws.com. NS
Answer
s3-eu-west-1.amazonaws.com. 5 NS ns-885.awsdns-46.net.
s3-eu-west-1.amazonaws.com. 5 NS ns-421.awsdns-52.com.
s3-eu-west-1.amazonaws.com. 5 NS ns-1546.awsdns-01.co.uk.
s3-eu-west-1.amazonaws.com. 5 NS ns-1258.awsdns-29.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0