Apex domains cannot have CNAME records.
Question and response
Question
dig cluster117.hosting.ovh.net. NS
Answer
cluster117.hosting.ovh.net. 5 NS ns100.ovh.net.
cluster117.hosting.ovh.net. 5 NS dns100.ovh.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0