Apex domains cannot have CNAME records.
Question and response
Question
dig dnsrubycom.com. NS
Answer
dnsrubycom.com. 4 NS ns08.domaincontrol.com.
dnsrubycom.com. 4 NS ns07.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0