.@ Tony Finch – blog

On Tuesday (2016-07-26) I gave a talk at work about domain registry APIs. It was mainly humorous complaining about needlessly complicated and broken stuff, but I slipped in a few cool ideas and recommendations for software I found useful.

I have published the slides and notes (both PDF).

The talk was based on what I learned last year when writing some software that I called superglue, but the talk wasn't about the software. That's what this article is about.

What is superglue?

Firstly, it isn't finished. To be honest, it's barely started! Which is why I haven't written about it before.

The goal is automated management of DNS delegations in parent zones - hence "super" (Latin for over/above/beyond, like a parent domain) "glue" (address records sometimes required as part of a delegation).

The basic idea is that superglue should work roughly like nsdiff | nsupdate.

Recall, nsdiff takes a DNS master file, and it produces an nsupdate script which makes the live version of the DNS zone match what the master file says it should be.

Similarly, superglue takes a collection of DNS records that describe a delegation, and updates the parent zone to match what the delegation records say it should be.

A uniform interface to several domain registries

Actually superglue is a suite of programs.

When I wrote it I needed to be able to update parent delegations managed by RIPE, JISC, Nominet, and Gandi; this year I have started moving our domains to Mythic Beasts. They all have different APIs, and only Nominet supports the open standard EPP.

So superglue has a framework which helps each program conform to a consistent command line interface.

Eventually there should be a superglue wrapper which knows which provider-specific script to invoke for each domain.

Refining the user interface

DNS delegation is tricky even if you only have the DNS to deal with. However, superglue also has to take into account the different rules that various domain registries require.

For example, in my initial design, the input to superglue was going to simply be the delegations records that should go in the parent zone, verbatim.

But some domain registries to not accept DS records; instead you have to give them your DNSKEY records, and the registry will generate their preferred form of DS records in the delegation. So superglue needs to take DNSKEY records in its input, and do its own DS generation for registries that require DS rather than DNSKEY.

Sticky problems

There is also a problem with glue records: my idea was that superglue would only need address records for nameservers that are within the domain whose delegation is being updated. This is the minimal set of glue records that the DNS requires, and in many cases it is easy to pull them out of the master file for the delegated zone.

However, sometimes a delegation includes name servers in a sibling domain. For example, cam.ac.uk and ic.ac.uk are siblings.

    cam.ac.uk.  NS  authdns0.csx.cam.ac.uk.
    cam.ac.uk.  NS  ns2.ic.ac.uk.
    cam.ac.uk.  NS  sns-pb.isc.org.
    ; plus a few more

In our delegation, glue is required for nameservers in cam.ac.uk, like authdns0; glue is forbidden for nameservers outside ac.uk, like sns-pb.isc.org. Those two rules are fixed by the DNS.

But for nameservers in a sibling domain, like ns2.ic.ac.uk, the DNS says glue may be present or omitted. Some registries say this optional sibling glue must be present; some registries say it must be absent.

In registries which require optional sibling glue, there is a quagmire of problems. In many cases the glue is already present, because it is part of the sibling delegation and, therefore, required - this is the case for ns2.ic.ac.uk. But when the glue is truly optional it becomes unclear who is responsible for maintaining it: the parent domain of the nameserver, or the domain that needs it for their delegation?

I basically decided to ignore that problem. I think you can work around it by doing a one-off manual set up of the optional glue, after which superglue will work. So it's similar to the other delegation management tasks that are out of scope for superglue, like registering or renewing domains.

Captain Adorable

The motivation for superglue was, in the short term, to do a bulk update of out 100+ delegations to add sns-pb.isc.org, and in the longer term, to support automatic DNSSEC key rollovers.

I wrote barely enough code to help with the short term goal, so what I have is undocumented, incomplete, and inconsistent. (Especially wrt DNSSEC support.)

And since then I haven't had time or motivation to work on it, so it remains a complete shambles.