Apex domains cannot have CNAME records.
Question and response
Question
dig gln.com. NS
Answer
gln.com. 5 NS ns-1150.awsdns-15.org.
gln.com. 5 NS ns-678.awsdns-20.net.
gln.com. 5 NS ns-363.awsdns-45.com.
gln.com. 5 NS ns-1636.awsdns-12.co.uk.
Authority
The response has no authority records.
Additional
ns-678.awsdns-20.net. 1 A 205.251.194.166
ns-1150.awsdns-15.org. 1 A 205.251.196.126
ns-1636.awsdns-12.co.uk. 1 A 205.251.198.100
ns-363.awsdns-45.com. 1 AAAA 2600:9000:5301:6b00:0:0:0:1
ns-678.awsdns-20.net. 1 AAAA 2600:9000:5302:a600:0:0:0:1
ns-1150.awsdns-15.org. 1 AAAA 2600:9000:5304:7e00:0:0:0:1
ns-1636.awsdns-12.co.uk. 1 AAAA 2600:9000:5306:6400:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0