Apex domains cannot have CNAME records.
Question and response
Question
dig rpworkshop.com. NS
Answer
rpworkshop.com. 5 NS ns-79.awsdns-09.com.
rpworkshop.com. 5 NS ns-351.awsdns-43.com.
rpworkshop.com. 5 NS ns-284.awsdns-35.com.
rpworkshop.com. 5 NS ns-201.awsdns-25.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0