Apex domains cannot have CNAME records.
Question and response
Question
dig str01.ru. NS
Answer
str01.ru. 5 NS ns01.xelent.cloud.
str01.ru. 5 NS ns02.xelent.cloud.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0