Apex domains cannot have CNAME records.
Question and response
Question
dig resolver.domains. NS
Answer
resolver.domains. 1 NS ns-505.awsdns-63.com.
resolver.domains. 1 NS ns-714.awsdns-25.net.
resolver.domains. 1 NS ns-1442.awsdns-52.org.
resolver.domains. 1 NS ns-1566.awsdns-03.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0