Apex domains cannot have CNAME records.
Question and response
Question
dig EDGECDN.RU. NS
Answer
EDGECDN.RU. 5 NS ns2.eccdn.co.
EDGECDN.RU. 5 NS ns1.edgecdn.ru.
Authority
The response has no authority records.
Additional
ns1.EDGECDN.RU. 5 A 5.188.176.176
ns1.EDGECDN.RU. 5 AAAA 2a11:27c0:1010:0:0:0:0:1176
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0