Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-40.net. NS
Answer
awsdns-40.net. 5 NS g-ns-489.awsdns-40.net.
awsdns-40.net. 5 NS g-ns-810.awsdns-40.net.
awsdns-40.net. 5 NS g-ns-1384.awsdns-40.net.
awsdns-40.net. 5 NS g-ns-1960.awsdns-40.net.
Authority
The response has no authority records.
Additional
g-ns-489.awsdns-40.net. 5 A 205.251.193.233
g-ns-810.awsdns-40.net. 5 A 205.251.195.42
g-ns-1384.awsdns-40.net. 5 A 205.251.197.104
g-ns-1960.awsdns-40.net. 5 A 205.251.199.168
g-ns-489.awsdns-40.net. 5 AAAA 2600:9000:5301:e900:0:0:0:1
g-ns-810.awsdns-40.net. 5 AAAA 2600:9000:5303:2a00:0:0:0:1
g-ns-1384.awsdns-40.net. 5 AAAA 2600:9000:5305:6800:0:0:0:1
g-ns-1960.awsdns-40.net. 5 AAAA 2600:9000:5307:a800:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0