Apex domains cannot have CNAME records.
Question and response
Question
dig s3-r-w.us-east-1.amazonaws.com. NS
Answer
s3-r-w.us-east-1.amazonaws.com. 5 NS ns-479.awsdns-59.com.
s3-r-w.us-east-1.amazonaws.com. 5 NS ns-1106.awsdns-10.org.
s3-r-w.us-east-1.amazonaws.com. 5 NS ns-537.awsdns-03.net.
s3-r-w.us-east-1.amazonaws.com. 5 NS ns-1567.awsdns-03.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0