Apex domains cannot have CNAME records.
Question and response
Question
dig smartcluster.net. NS
Answer
smartcluster.net. 4 NS ns-1067.awsdns-05.org.
smartcluster.net. 4 NS ns-867.awsdns-44.net.
smartcluster.net. 4 NS ns-312.awsdns-39.com.
smartcluster.net. 4 NS ns-1691.awsdns-19.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0