Apex domains cannot have CNAME records.
Question and response
Question
dig linode-de.qualityunit.com. NS
Answer
linode-de.qualityunit.com. 5 NS pdns3.qualityunit.com.
linode-de.qualityunit.com. 5 NS pdns4.qualityunit.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0