## Summary
This PR adds a new domain modifier `IGNORE_EXTERNAL_DNS()` that
automatically detects and ignores DNS records managed by Kubernetes
[external-dns](https://github.com/kubernetes-sigs/external-dns)
controller.
**Related Issue:** This addresses the feature request discussed in
StackExchange/dnscontrol#935 (Idea: Ownership system), where
@tlimoncelli indicated openness to accepting a PR for this
functionality.
## Problem
When running DNSControl alongside Kubernetes external-dns, users face a
challenge:
- **external-dns** dynamically creates DNS records based on Kubernetes
Ingress/Service resources
- Users cannot use `IGNORE()` because they cannot predict which record
names external-dns will create
- Using `NO_PURGE()` is too broad - it prevents DNSControl from cleaning
up any orphaned records
The fundamental issue is that `IGNORE()` requires static patterns known
at config-time, but external-dns creates records dynamically at runtime.
## Solution
`IGNORE_EXTERNAL_DNS()` solves this by detecting external-dns managed
records at runtime:
```javascript
D("example.com", REG_CHANGEME, DnsProvider(DSP_MY_PROVIDER),
IGNORE_EXTERNAL_DNS(), // Automatically ignore external-dns managed records
A("@", "1.2.3.4"),
CNAME("www", "@")
);
```
### How It Works
external-dns uses a TXT record registry to track ownership. For each
managed record, it creates a TXT record like:
- `a-myapp.example.com` → TXT containing
`heritage=external-dns,external-dns/owner=...`
- `cname-api.example.com` → TXT containing
`heritage=external-dns,external-dns/owner=...`
This PR:
1. Scans existing TXT records for the `heritage=external-dns` marker
2. Parses the TXT record name prefix (e.g., `a-`, `cname-`) to determine
the managed record type
3. Automatically adds those records to the ignore list during diff
operations
## Changes
| File | Purpose |
|------|---------|
| `models/domain.go` | Add `IgnoreExternalDNS` field to DomainConfig |
| `pkg/js/helpers.js` | Add `IGNORE_EXTERNAL_DNS()` JavaScript helper |
| `pkg/diff2/externaldns.go` | Core detection logic for external-dns TXT
records |
| `pkg/diff2/externaldns_test.go` | Unit tests for detection logic |
| `pkg/diff2/handsoff.go` | Integrate external-dns detection into
handsoff() |
| `pkg/diff2/diff2.go` | Pass IgnoreExternalDNS flag to handsoff() |
| `commands/types/dnscontrol.d.ts` | TypeScript definitions for IDE
support |
| `documentation/.../IGNORE_EXTERNAL_DNS.md` | User documentation |
## Design Philosophy
This follows DNSControl's pattern of convenience builders (like
`M365_BUILDER`, `SPF_BUILDER`, `DKIM_BUILDER`) that make complex
operations simple. Just as those builders abstract away implementation
details, `IGNORE_EXTERNAL_DNS()` abstracts away the complexity of
detecting external-dns managed records.
## Testing
All unit tests pass:
```
go test ./pkg/diff2/... -v # Tests detection logic
go test ./pkg/js/... # Tests JS helpers
go build ./... # Builds successfully
```
## Caveats Documented
- Only supports TXT registry (the default for external-dns)
- Requires external-dns to use default naming conventions
- May need updates if external-dns changes its registry format
---------
Co-authored-by: Tom Limoncelli <6293917+tlimoncelli@users.noreply.github.com>
