Writing new DNS providers

Writing a new DNS provider is a relatively straightforward process. You essentially need to implement the providers.DNSServiceProvider interface. and the system takes care of the rest.

Please do note that if you submit a new provider you will be assigned bugs related to the provider in the future (unless you designate someone else as the maintainer). More details here.

Overview

I’ll ignore all the small stuff and get to the point.

A provider’s GetDomainCorrections() function is the workhorse of the provider. It is what gets called by dnscontrol preview and dnscontrol push.

How does a provider’s GetDomainCorrections() function work?

The goal of GetDomainCorrections() is to return a list of corrections. Each correction is a text string describing the change (“Delete CNAME record foo”) and a function that, if called, will make the change (i.e. call the API and delete record foo). Preview mode simply prints the text strings. dnscontrol push prints the strings and calls the functions. Because of how Go’s functions work, the function will have everything it needs to make the change. Pretty cool, eh?

So how does GetDomainCorrections() work?

First, some terminology: The DNS records specified in the dnsconfig.js file are called the “desired” records. The DNS records stored at the DNS service provider are called the “existing” records.

Every provider does the same basic process. The function GetDomainCorrections() is called with a list of the desired DNS records (dc.Records). It then contacts the provider’s API and gathers the existing records. It converts the existing records into a list of *models.RecordConfig.

Now that it has the desired and existing records in the appropriate format, differ.IncrementalDiff(existingRecords) is called and does all the hard work of understanding the DNS records and figuring out what changes need to be made. It generates lists of adds, deletes, and changes.

GetDomainCorrections() then generates the list of models.Corrections() and returns. DNSControl takes care of the rest.

So, what does all this mean?

It basically means that writing a provider is as simple as writing code that (1) downloads the existing records, (2) converts each records into models.RecordConfig, (3) write functions that perform adds, changes, and deletions.

If you are new to Go, there are plenty of providers you can copy from. In fact, many non-Go programmers have learned Go by contributing to DNSControl.

Oh, and what if the API simply requires that the entire zonefile be uploaded every time? We still generate the text descriptions of the changes (so that dnscontrol preview looks nice) but the functions are just no-ops, except for one that uploads the new zonefile.

Now that you understand the general process, here are the details.

Step 1: General advice

A provider can be a DnsProvider, a Registrar, or both. We recommend you write the DnsProvider first, release it, and then write the Registrar if needed.

If you have any questions, please dicuss them in the Github issue related to the request for this provider. Please let us know what was confusing so we can update this document with advice for future authors (or even better, update this document yourself.)

Step 2: Pick a base provider

Pick a similar provider as your base. Providers basically fall into three general categories:

TODO: Categorize DNSIMPLE, NAMECHEAP

All providers use the “diff” module to detect differences. It takes two zones and returns records that are unchanged, created, deleted, and modified. The incremental providers use the differences to update individual records or recordsets. The zone providers use the information to print a human-readable list of what is being changed, but upload the entire new zone.

Step 3: Create the driver skeleton

Create a directory for the provider called providers/name where name is all lowercase and represents the commonly-used name for the service.

The main driver should be called providers/name/nameProvider.go. The API abstraction is usually in a separate file (often called api.go).

Step 4: Activate the driver

Edit providers/_all/all.go. Add the provider list so DNSControl knows it exists.

Step 5: Implement

Implement all the calls in providers.DNSServiceProvider interface..

The function GetDomainCorrections is a bit interesting. It returns a list of corrections to be made. These are in the form of functions that DNSControl can call to actually make the corrections.

Step 6: Unit Test

Make sure the existing unit tests work. Add unit tests for any complex algorithms in the new code.

Run the unit tests with this command:

cd dnscontrol
go test ./...

Step 7: Integration Test

This is the most important kind of testing when adding a new provider. Integration tests use a test account and a real domain.

For example, this will run the tests using BIND:

cd dnscontrol/integrationTest
go test -v -verbose -provider BIND

(BIND is a good place to start since it doesn’t require any API keys.)

This will run the tests on Amazon AWS Route53:

export R53_DOMAIN=dnscontroltest-r53.com  # Use a test domain.
export R53_KEY_ID=CHANGE_TO_THE_ID
export R53_KEY='CHANGE_TO_THE_KEY'
go test -v -verbose -provider ROUTE53

Step 5: Update docs

Step 6: Submit a PR

At this point you can submit a PR.

Actually you can submit the PR even earlier if you just want feedback, input, or have questions. This is just a good stopping place to submit a PR if you haven’t already.

Step 7: Capabilities

Some DNS providers have features that others do not. For example some support the SRV record. A provider announces what it can do using the capabilities system.

If a provider doesn’t advertise a particular capability, the integration test system skips the appropriate tests. Therefore you might want to initially develop the provider with no particular capabilities advertised and code until all the integration tests work. Then enable capabilities one at a time to finish off the project.

Don’t feel obligated to implement everything at once. In fact, we’d prefer a few small PRs than one big one. Focus on getting the basic provider working well before adding these extras.

Operational features have names like providers.CanUseSRV and providers.CanUseAlias. The list of optional “capabilities” are in the file dnscontrol/providers/providers.go (look for CanUseAlias).

Capabilities are processed early by DNSControl. For example if a provider doesn’t support SRV records, DNSControl will error out when parsing dnscontrol.js rather than waiting until the API fails at the very end.

Enable optional capabilities in the nameProvider.go file and run the integration tests to see what works and what doesn’t. Fix any bugs and repeat, repeat, repeat until you have all the capabilities you want to implement.

FYI: If a provider’s capabilities changes, run go generate to update the documentation.

Vendoring Dependencies

If your provider depends on other go packages, then you must vendor them. To do this, use govendor. A command like this is usually suffient:

go get github.com/kardianos/govendor
govendor add +e