Apex domains cannot have CNAME records.
Question and response
Question
dig eu-central-1.elb.amazonaws.com. NS
Answer
eu-central-1.elb.amazonaws.com. 5 NS ns-1689.awsdns-19.co.uk.
eu-central-1.elb.amazonaws.com. 5 NS ns-417.awsdns-52.com.
eu-central-1.elb.amazonaws.com. 5 NS ns-613.awsdns-12.net.
eu-central-1.elb.amazonaws.com. 5 NS ns-1326.awsdns-37.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0