Apex domains cannot have CNAME records.
Question and response
Question
dig zenoss.io. NS
Answer
zenoss.io. 5 NS ns-cloud-d3.googledomains.com.
zenoss.io. 5 NS ns-cloud-d1.googledomains.com.
zenoss.io. 5 NS ns-cloud-d2.googledomains.com.
zenoss.io. 5 NS ns-cloud-d4.googledomains.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0