Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-21.net. NS
Answer
awsdns-21.net. 5 NS g-ns-1365.awsdns-21.net.
awsdns-21.net. 5 NS g-ns-1941.awsdns-21.net.
awsdns-21.net. 5 NS g-ns-470.awsdns-21.net.
awsdns-21.net. 5 NS g-ns-791.awsdns-21.net.
Authority
The response has no authority records.
Additional
g-ns-470.awsdns-21.net. 5 A 205.251.193.214
g-ns-791.awsdns-21.net. 5 A 205.251.195.23
g-ns-1365.awsdns-21.net. 5 A 205.251.197.85
g-ns-1941.awsdns-21.net. 5 A 205.251.199.149
g-ns-470.awsdns-21.net. 5 AAAA 2600:9000:5301:d600:0:0:0:1
g-ns-791.awsdns-21.net. 5 AAAA 2600:9000:5303:1700:0:0:0:1
g-ns-1365.awsdns-21.net. 5 AAAA 2600:9000:5305:5500:0:0:0:1
g-ns-1941.awsdns-21.net. 5 AAAA 2600:9000:5307:9500:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0