Cannot add CNAME record with existing record of same name: This record will conflict with the glue record for the zone

Symptoms

• Can't add CNAME record for a domain or subdomain via the Plesk GUI, with the following error displayed:

  PLESK_ERROR: This record will conflict with the glue record for the zone

• There's an existing record of a different type of DNS record (A, MX, NS, TXT) with the same name within the DNS zone of the affected domain.

Cause:

This is expected behavior that complies with RFC1912, which states that a CNAME record cannot coexist with other records (types A, NS, MX, TXT) that have the exact same domain as the CNAME record, because they effectively overwrite all other records with the exact same domain.

Solution:

Remove the duplicate record or add it with a prefix (for example www.) in the Host column of the DNS zone by using the steps in this article:

How to edit DNS zone records for a Plesk domain?

Alternatively, recreate the domain as an alias with with its own completely separate DNS zone.