dnscontrol/docs/adding-new-rtypes.md

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Creating new DNS Resource Types (Rtypes)

Everyone is familiar with A, AAAA, CNAME, NS and other Rtypes. However there are new record types being added all the time (possibly too many). Each new record type requires special handling by DNSControl.

If a record simply has a single "target", then there is little to do because it is handled similarly to A, CNAME, and so on. However if there are multiple fields within the record you have more work to do.

Our general philosophy is:

• Internally the individual fields of a record are kept separate. If a particular provider combines them into one big string, that kind of thing is done in the provider code at the end of the food chain. For example, an MX record has a Target (aspmx.l.google.com.) and a preference (10). Some systems combine this into one string (10 aspmx.l.google.com.). We keep the two values separate in RecordConfig and leave it up to the individual providers to merge them when required. An earlier implementation kept everything combined and we found ourselves constantly parsing and re-parsing the target. It was inefficient and lead to many bugs.
• Anywhere we have a special case for a particular Rtype, we use a switch statement and have a case for every single record type, usually with a default: case that calls panic(). This way developers adding a new record type will quickly find where they need to add code (the panic will tell them where). Before we did this, missing implementation code would go unnoticed for months.
• Keep things alphabetical. If you are adding your record type to a case statement, function library, or whatever, please list it alphabetically along with the others when possible.

Step 1: Update RecordConfig in models/dns.go

If the record has any unique fields, add them to RecordConfig. The field name should be the record type, then the field name as used in github.com/miekg/dns/types.go. For example, the CAA record has a field called Flag, therefore the field name in RecordConfig is CaaFlag (not CaaFlags or CAAFlags).

Here are some examples:

type RecordConfig struct {
  ...
  MxPreference uint16            `json:"mxpreference,omitempty"` // FIXME(tlim): Rename to MxPreference
  SrvPriority  uint16            `json:"srvpriority,omitempty"`
  SrvWeight    uint16            `json:"srvweight,omitempty"`
  SrvPort      uint16            `json:"srvport,omitempty"`
  CaaTag       string            `json:"caatag,omitempty"`
  CaaFlag      uint8             `json:"caaflag,omitempty"`
  ...
}

Step 2: Add a capability for the record

You'll need to mark which providers support this record type. The initial PR should implement this record for the bind provider at a minimum.

• Add the capability to the file dnscontrol/providers/providers.go (look for CanUseAlias and add it to the end of the list.)
• Mark the bind provider as supporting this record type by updating dnscontrol/providers/bind/bindProvider.go (look for providers.CanUs and you'll see what to do).

Step 2: Add a helper function

Add a function to pkg/js/helpers.js for the new record type. This is the Javascript file that defines dnsconfig.js's functions like A() and MX(). Look at the definition of A, MX and CAA for good examples to use as a base.

Please add the function alphabetically with the others. Also, please run prettier on the file to ensure your code conforms to our coding standard:

npm install prettier node_modules/.bin/prettier --write pkg/js/helpers.js

Step 3: Search for #rtype_variations

Anywhere a rtype requires special handling has been marked with a comment that includes the string #rtype_variations. Search for this string and add your new type to this code.

Step 4: Add a parse_tests test case.

Add at least one test case to the pkg/js/parse_tests directory. Test 013-mx.js is a very simple one and is good for cloning.

Run these tests via:

cd dnscontrol/pkg/js
go test ./...

If this works, then you know the dnsconfig.js and helpers.js code is working correctly.

As you debug, if there are places that haven't been marked #rtype_variations that should be, add such a comment. Every time you do this, an angel gets its wings.

Step 5: Add an integrationTest test case.

Add at least one test case to the integrationTest/integration_test.go file. Look for var tests = and add the test to the end of this list.

Each entry in the list is a new state. For example:

  //MX
  tc("Empty"),                                    <<< 1
  tc("MX record", mx("@", 5, "foo.com.")),        <<< 2
  tc("Change MX pref", mx("@", 10, "foo.com.")),  <<< 3

Line 1: An tc() entry with no records (just a comment). The test system will delete all records from the domain to make the domain match this empty configuration. This creates a "clean slate" situation.

Line 2: A tc() entry with 1 record. To get to this state, the provider will have to add the record. If this works, basic functionality for the MX record type has been achieved.

Line 3: A tc() entry with 1 record, with a different priority. To get to this state, the provider will have to either change the priority on an existing record, or delete the old record and insert a new one. Either way, this test case assures us that the diff'ing functionality is working properly.

If you look at the tests for CAA, it inserts a few records then attempts to modify each field of a record one at a time. This test was useful because it turns out we hadn't written the code to properly see a change in priority. We fixed this bug before the code made it into production.

Also notice that some tests include .IfHasCapability(). This limits the test to providers with certain capabilities. You'll want to use this feature so that the tests only run on providers that support your new record type.

To run the integration test with the BIND provider:

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

Once the code works for BIND, consider submitting a PR at this point.

As you debug, if there are places that haven't been marked #rtype_variations that should be, add such a comment. If you fail to do this, God kills a cute little kitten.

Step 6: Support more providers

Now add support other providers. Add the providers.CanUse... flag to the provider and re-run the integration tests:

For example, 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