Apex domains cannot have CNAME records.
Question and response
Question
dig oraclecloud.com. NS
Answer
oraclecloud.com. 5 NS n2-a18.aka-ns.net.
oraclecloud.com. 5 NS ns3.p201.dns.oraclecloud.net.
oraclecloud.com. 5 NS n2-a11.aka-ns.net.
oraclecloud.com. 5 NS ns1.p201.dns.oraclecloud.net.
oraclecloud.com. 5 NS ns4.p201.dns.oraclecloud.net.
oraclecloud.com. 5 NS ns2.p201.dns.oraclecloud.net.
oraclecloud.com. 5 NS n2-a1.aka-ns.net.
oraclecloud.com. 5 NS n2-a13.aka-ns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0