Apex domains cannot have CNAME records.
Question and response
Question
dig rudc.cloud. NS
Answer
rudc.cloud. 5 NS beta.atlex.ru.
rudc.cloud. 5 NS alpha.atlex.ru.
rudc.cloud. 5 NS gamma.atlex.ru.
Authority
The response has no authority records.
Additional
beta.atlex.ru. 5 A 193.161.84.90
alpha.atlex.ru. 5 A 91.109.200.200
gamma.atlex.ru. 5 A 188.226.189.38
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0