Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-51.org. NS
Answer
awsdns-51.org. 5 NS g-ns-757.awsdns-51.org.
awsdns-51.org. 5 NS g-ns-179.awsdns-51.org.
awsdns-51.org. 5 NS g-ns-1651.awsdns-51.org.
awsdns-51.org. 5 NS g-ns-1078.awsdns-51.org.
Authority
The response has no authority records.
Additional
g-ns-179.awsdns-51.org. 5 A 205.251.192.179
g-ns-757.awsdns-51.org. 5 A 205.251.194.245
g-ns-1078.awsdns-51.org. 5 A 205.251.196.54
g-ns-1651.awsdns-51.org. 5 A 205.251.198.115
g-ns-179.awsdns-51.org. 5 AAAA 2600:9000:5300:b300:0:0:0:1
g-ns-757.awsdns-51.org. 5 AAAA 2600:9000:5302:f500:0:0:0:1
g-ns-1078.awsdns-51.org. 5 AAAA 2600:9000:5304:3600:0:0:0:1
g-ns-1651.awsdns-51.org. 5 AAAA 2600:9000:5306:7300:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0