Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-51.net. NS
Answer
awsdns-51.net. 5 NS g-ns-500.awsdns-51.net.
awsdns-51.net. 5 NS g-ns-1971.awsdns-51.net.
awsdns-51.net. 5 NS g-ns-1395.awsdns-51.net.
awsdns-51.net. 5 NS g-ns-821.awsdns-51.net.
Authority
The response has no authority records.
Additional
g-ns-500.awsdns-51.net. 5 A 205.251.193.244
g-ns-821.awsdns-51.net. 5 A 205.251.195.53
g-ns-1395.awsdns-51.net. 5 A 205.251.197.115
g-ns-1971.awsdns-51.net. 5 A 205.251.199.179
g-ns-500.awsdns-51.net. 5 AAAA 2600:9000:5301:f400:0:0:0:1
g-ns-821.awsdns-51.net. 5 AAAA 2600:9000:5303:3500:0:0:0:1
g-ns-1395.awsdns-51.net. 5 AAAA 2600:9000:5305:7300:0:0:0:1
g-ns-1971.awsdns-51.net. 5 AAAA 2600:9000:5307:b300:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0