Apex domains cannot have CNAME records.
Question and response
Question
dig sharedrule.com. NS
Answer
sharedrule.com. 5 NS ns-903.awsdns-48.net.
sharedrule.com. 5 NS ns-86.awsdns-10.com.
sharedrule.com. 5 NS ns-714.awsdns-25.net.
sharedrule.com. 5 NS ns-881.awsdns-46.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0