ALIAS (CNAME flattening)

An ALIAS record is a provider-side feature that lets you point a hostname (including the zone apex, like example.com) at another hostname the way a CNAME does, while still returning A/AAAA answers to clients.

Different providers use different names for the same idea:

• Cloudflare commonly describes this as “CNAME flattening”
• Other DNS providers may call it ALIAS, ANAME, or flattened CNAME

Use ALIAS when you want “point this name at that hostname” behavior but you can’t (or shouldn’t) use CNAME, most commonly:

• At the zone apex (example.com) where CNAME is not allowed by standard DNS rules.
• When you want the convenience of targeting a hostname that may change IPs (CDNs, hosted services), but still need clients to receive A/AAAA records.

• Name: the hostname inside the zone you’re creating the record for.
  • For the zone apex, many DNS tools use @ (BIND/zone-file notation) to mean “the zone root”.
  • For a subdomain, use the label (for example www for www.example.com).
• Value: a target hostname (FQDN), like myapp.hosting-provider.com.
  • ALIAS values should be hostnames, not IP addresses.
  • The target hostname should ultimately resolve to A and/or AAAA records (directly or through other DNS indirection).

ALIAS does not exist as a standardized DNS RRType that recursive resolvers understand everywhere. Instead, the DNS provider’s authoritative system does the work:

1. A client’s recursive resolver asks for A and/or AAAA for the ALIAS name (for example example.com).
2. Datum resolves the ALIAS target hostname (for example myapp.hosting-provider.com) to its current A/AAAA records.
3. Datum returns the resulting A/AAAA answers as if they were directly configured on the ALIAS name.

Important consequence: clients typically do not see a CNAME in the response. They see A/AAAA records for the name they queried.

• CNAME: returns a CNAME response and relies on the resolver to chase it.
• ALIAS / “CNAME flattening”: returns A/AAAA directly (synthesized by the DNS provider).

• Portability: ALIAS/flattening is not uniform across providers. If you move DNS providers, you may need to translate this into whatever equivalent that provider supports.
• Answer types: ALIAS is primarily about synthesizing A/AAAA answers. It is not a general replacement for other record types.