Apex domains cannot have CNAME records.
Question and response
Question
dig srv.ambientia.fi. NS
Answer
srv.ambientia.fi. 1 NS luke.ns.cloudflare.com.
srv.ambientia.fi. 1 NS amber.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0