Apex domains cannot have CNAME records.
Question and response
Question
dig riera-sj.com. NS
Answer
riera-sj.com. 5 NS ns-879.awsdns-45.net.
riera-sj.com. 5 NS ns-155.awsdns-19.com.
riera-sj.com. 5 NS ns-374.awsdns-46.com.
riera-sj.com. 5 NS ns-1401.awsdns-47.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0