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ALIAS records are virtual alias records resolved at the time of each request - providing "flattened" (no CNAME-record chain) synthesized records with data from a hidden source name.

This can be used for different purposes - including solving the classic problem with CNAME-records at the domain apex/root (for the zone name / for "the naked domain").

Say you want to host a website at a domain name without the "www" (or other) prefix. The IP address for the web-server is not static (subject to change) - only a static host name is provided for the web-server. This is a common scenario with many cloud services today including Azure VMs, GitHub pages, Heroku, etc. The solution that often springs to mind, is to configure a CNAME-record for your domain name pointing to the static host name provided by the cloud service. Unfortunately this is not possible because such a CNAME-record would conflict with other records that are always present for the zone name (SOA / NS).

Now you can do this by using an ALIAS-record instead.

ALIAS records are similar to CNAME-records. The difference is that ALIAS records are resolved and synthesized into the requested record type (such as A-records) by the authoritative DNS server instead of by the client / resolving DNS server, and an ALIAS-record is tied to a specific record type (such as A-records) and therefore does not conflict with other records with the same name but of a type other than what the ALIAS-record is tied to.

You can use the CNAME-record in the normal edit zone form or the raw form on our servers. The format in which to enter the data is as follows:

ALIAS A (IPv4):
@ ALIAS A cloudserviceprovider.com.

ALIAS AAAA (IPv6):
@ ALIAS AAAA cloudserviceprovider.com.

ALIAS MX:
@ ALIAS MX mx1.cloudserviceprovider.com.


Where cloudserviceprovider.com is the domain name of the website/cloud service you wish to alias to.

Features / Benefits:

CNAME chain flattening

When using large cloud service providers, DNS host names often point to a chain of CNAME records. Each client (or their DNS resolver) has to resolve each one of these CNAMEs - delaying access to your service. By using an ALIAS-record, you basically move this work to your own DNS server and provide clients with "flattened" records (all interim CNAME-records are removed / hidden), and thereby provide faster access for your clients.

Multiple ALIAS records for same name / same type

You can have multiple ALIAS records for the same name and record type - resolving records from multiple names and combining the results into one synthesized record set. And yes, this works very well with the round robin option for load balancing.

Multiple ALIAS records for same name / different types

You can have multiple ALIAS records for the same name but different record types.
For example: yourname.com / A-records -> "webserv1.cloudoperator.com", and yourname.com / MX-records -> "smtp.othercompany.com".

Wildcard records

ALIAS records can also be wildcard records (*.example.com). Easy way to provide records for many sub-names.

TTL

The TTL (Time To Live) value for an ALIAS-record is a maximum value. A synthesized record provided to the client will have a TTL value reflecting the lowest TTL value of all the records that were used (including any interim CNAME records). This ensures that clients will not cache stale data.

Considerations:

Proprietary / non-standard

The ALIAS-record type is a proprietary / non-standard record type - not understood by other DNS server / resolver implementations. Generally, this is not a problem because ALIAS records are synthesized into other (standard) record types before they leave our servers. This only becomes an issue if the raw zone data is shared with other DNS server implementations - for example through secondary zone transfers (see "Secondary DNS servers" below).

Secondary DNS servers

ALIAS records may not be served correctly if secondary DNS servers for the containing zone are not compatible with our implementation of ALIAS records.

DNSSEC

ALIAS records are not compatible with DNSSEC. Signing a zone containing ALIAS records will not work correctly.

Other implementations:

Similar implementations of virtual alias records ("ANAME", "ALIAS", "CNAME flattening") are offered by various DNS service providers. These are generally not compatible with each other. There is no standard (RFC or similar) for this.



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