Record aliases/CNAME flattening

[csmith]

It'd be nice to support something like Cloudflare's CNAME flattening, allowing the root domain of a zone to be effectively aliased to a subdomain (or, perhaps, a different domain also hosted my mydnshost?).

Instead of overloading and confusing CNAME records, I think having something like an 'ALIAS' record type would be nice. The records can then be copied when the zone(s) are changed (so it's all transparent to Bind).

[ShaneMcC]

I think a dedicated ALIAS record that we then do special-processing on is the best way to go with this.

My initial thoughts are that at zone-compile time we just do an AAAA/A lookup then write those out instead of the ALIAS record.

This lets us be more flexible (allows us to point anywhere not just records hosted with us) but there are some issues:

• Circular dependencies on ALIAS records will resolve strangely
• How often do we refresh the ALIAS
• Anything that gets ALIASed that normally does dns-based load balancing is going to get balanced based on the location of our web frontend, not the remote user.

[ShaneMcC]

https://tools.ietf.org/html/draft-ietf-dnsop-aname-01 will also solve this if it happens before I do anything hacky...

[ShaneMcC]

ANAME poses interesting DNSSEC challenges for auto-signing, if the slave servers don't have the DNSSEC keys they can't sign an ANAME record... hmm.

[ShaneMcC]

Looks like the ANAME spec already considers that. The master does the resolving and returns ANAME and A/AAAA records in zone transfers so that the secondary servers are able to return signed A/AAAA responses. Would result in #62 being more important as our database-serial may be significantly lower than the real serial after a while.

[ShaneMcC]

If we ever do this, think of: #131 (ipv4hint and ipv6hint on SVCB/HTTPS records)