Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-21.org. NS
Answer
awsdns-21.org. 5 NS g-ns-149.awsdns-21.org.
awsdns-21.org. 5 NS g-ns-727.awsdns-21.org.
awsdns-21.org. 5 NS g-ns-1048.awsdns-21.org.
awsdns-21.org. 5 NS g-ns-1621.awsdns-21.org.
Authority
The response has no authority records.
Additional
g-ns-149.awsdns-21.org. 5 A 205.251.192.149
g-ns-727.awsdns-21.org. 5 A 205.251.194.215
g-ns-1048.awsdns-21.org. 5 A 205.251.196.24
g-ns-1621.awsdns-21.org. 5 A 205.251.198.85
g-ns-149.awsdns-21.org. 5 AAAA 2600:9000:5300:9500:0:0:0:1
g-ns-727.awsdns-21.org. 5 AAAA 2600:9000:5302:d700:0:0:0:1
g-ns-1048.awsdns-21.org. 5 AAAA 2600:9000:5304:1800:0:0:0:1
g-ns-1621.awsdns-21.org. 5 AAAA 2600:9000:5306:5500:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0