Apex domains cannot have CNAME records.
Question and response
Question
dig pod29.euw1.zdsys.com. NS
Answer
pod29.euw1.zdsys.com. 5 NS ns-1840.awsdns-38.co.uk.
pod29.euw1.zdsys.com. 5 NS ns-242.awsdns-30.com.
pod29.euw1.zdsys.com. 5 NS ns-1007.awsdns-61.net.
pod29.euw1.zdsys.com. 5 NS ns-1144.awsdns-15.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0