Apex domains cannot have CNAME records.
Question and response
Question
dig aws-198.aws.melbourneit.com.au. NS
Answer
aws-198.aws.melbourneit.com.au. 4 NS ns-194.awsdns-24.com.
aws-198.aws.melbourneit.com.au. 4 NS ns-1420.awsdns-49.org.
aws-198.aws.melbourneit.com.au. 4 NS ns-697.awsdns-23.net.
aws-198.aws.melbourneit.com.au. 4 NS ns-1724.awsdns-23.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0