Apex domains cannot have CNAME records.
Question and response
Question
dig s3-r-w.us-west-2.amazonaws.com. NS
Answer
s3-r-w.us-west-2.amazonaws.com. 5 NS ns-1144.awsdns-15.org.
s3-r-w.us-west-2.amazonaws.com. 5 NS ns-1997.awsdns-57.co.uk.
s3-r-w.us-west-2.amazonaws.com. 5 NS ns-352.awsdns-44.com.
s3-r-w.us-west-2.amazonaws.com. 5 NS ns-546.awsdns-04.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0