Apex domains cannot have CNAME records.
Question and response
Question
dig exoscale.io. NS
Answer
exoscale.io. 5 NS ns-1-b.gandi.net.
exoscale.io. 5 NS ns-60-a.gandi.net.
exoscale.io. 5 NS ns-60-c.gandi.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0