Apex domains cannot have CNAME records.
Question and response
Question
dig azurewebsites.net. NS
Answer
azurewebsites.net. 5 NS ns4-224.azure-dns.info.
azurewebsites.net. 5 NS ns1-224.azure-dns.com.
azurewebsites.net. 5 NS ns2-224.azure-dns.net.
azurewebsites.net. 5 NS ns3-224.azure-dns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0