feat(azure): dns metadata (tags) support

[vaspoz]

What does it do ?

This PR adds support for Azure DNS metadata (tags) in external-dns. Users can now annotate Kubernetes resources with external-dns.alpha.kubernetes.io/azure-metadata-* annotations to set Azure resource tags on the corresponding DNS records.

Motivation

Azure DNS records support metadata (tags) for resource organization, cost tracking, and compliance. This feature enables Kubernetes users to manage DNS record tags declaratively through annotations, making it easier to:

• Track which Kubernetes resources created which DNS records
• Organize DNS records by environment, team, or cost center
• Implement governance and compliance policies at the DNS level

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

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• ✅ login: vaspoz / name: Basil Pozdeev (1628f16, 83edb29, 9e08a42)

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[vflaux]

/ok-to-test

[coveralls]

Pull Request Test Coverage Report for Build 19870223885

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 72 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.02%) to 78.687%

---

Files with Coverage Reduction	New Missed Lines	%
apis/externaldns/types.go	1	99.71%
plan.go	3	95.85%
coredns/coredns.go	31	90.36%
azure/azure.go	37	80.37%

Totals
Change from base Build 19788190926:	0.02%
Covered Lines:	16038
Relevant Lines:	20382

---

💛 - Coveralls

[ivankatliarchuk]

Hi. Could you share similar results for this PR #5085 (comment). Need to make sure it works before we merge. What we looking as well, where or not the behaviour works when tags added, deleted, modified.

[vflaux]

Hi,
You could add test cases in TestAzureApplyChanges() like this one:

	endpoint.NewEndpointWithTTL("metadata.example.com", endpoint.RecordTypeA, endpoint.TTL(recordTTL), "1.2.3.4").
			WithProviderSpecific("azure-metadata-foo", "bar").
			WithProviderSpecific("azure-metadata-baz", "qux"),

This should cover your code without adding new tests.

[vaspoz]

@ivankatliarchuk , here's the tests outputs:
Test A: Add new metadata

1. Create HTTPRoute:

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: test-metadata-add
  annotations:
    external-dns.alpha.kubernetes.io/azure-metadata-environment: production
    external-dns.alpha.kubernetes.io/azure-metadata-team: platform
    external-dns.alpha.kubernetes.io/azure-metadata-cost-center: "12345"
spec:
  hostnames:
    - metadata-test.basil.sbx.org.cloud
  parentRefs:
    - name: internal
      namespace: istio-system
      sectionName: https
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /
      backendRefs:
        - name: dummy-service
          port: 80

2. Check the resources:

❯ az network dns record-set a show \
  --resource-group $RESOURCE_GROUP \
  --zone-name $DNS_ZONE \
  --name metadata-test \
  --query "metadata" \
  -o json
---
{
  "cost-center": "12345",
  "environment": "production",
  "team": "platform"
}

Test B: Update metadata

1. Apply updated manifest:

# Test Case 2: Modify Metadata Tags on an Existing DNS Record
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: test-metadata-add
  annotations:
    external-dns.alpha.kubernetes.io/azure-metadata-environment: staging
    external-dns.alpha.kubernetes.io/azure-metadata-team: backend
    external-dns.alpha.kubernetes.io/azure-metadata-owner: john-doe
    # cost-center annotation removed
spec:
  hostnames:
    - metadata-test.basil.sbx.org.cloud
  parentRefs:
    - name: internal
      namespace: istio-system
      sectionName: https
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /
      backendRefs:
        - name: dummy-service
          port: 80

2. Check the metadata:

❯ az network dns record-set a show \
  --resource-group $RESOURCE_GROUP \
  --zone-name $DNS_ZONE \
  --name metadata-test \
  --query "metadata" \
  -o json
---
{
  "environment": "staging",
  "owner": "john-doe",
  "team": "backend"
}

Test C: Delete metadata

1. Apply udpated manifest:

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: test-metadata-add
  annotations:
    # All azure-metadata-* annotations removed
spec:
  hostnames:
    - metadata-test.basil.sbx.org.cloud
  parentRefs:
    - name: internal
      namespace: istio-system
      sectionName: https
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /
      backendRefs:
        - name: dummy-service
          port: 80

2. Check the metadata:

❯ az network dns record-set a show \
  --resource-group $RESOURCE_GROUP \
  --zone-name $DNS_ZONE \
  --name metadata-test \
  --query "metadata" \
  -o json
---
<no output>

Test D: Special characters

1. Apply new manifest:

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: test-metadata-special
  annotations:
    external-dns.alpha.kubernetes.io/azure-metadata-description: "Test service for app-v2.0"
    external-dns.alpha.kubernetes.io/azure-metadata-contact-email: "[email protected]"
spec:
  hostnames:
    - metadata-special.basil.sbx.org.cloud
  parentRefs:
    - name: internal
      namespace: istio-system
      sectionName: https
  rules:
    - matches:
        - path:
            type: PathPrefix
            value: /
      backendRefs:
        - name: dummy-service
          port: 80

2. Check the metadata:

❯ az network dns record-set a show \
  --resource-group $RESOURCE_GROUP \
  --zone-name $DNS_ZONE \
  --name metadata-special \
  --query "metadata" \
  -o json
---
{
  "contact-email": "[email protected]",
  "description": "Test service for app-v2.0"
}

Logs:

time="2025-12-02T17:15:53Z" level=info msg="Updating A record named 'metadata-test' to '9.163.156.200' for Azure DNS zone 'basil.sbx.org.cloud'."
time="2025-12-02T17:15:53Z" level=info msg="Updating TXT record named 'a-metadata-test' to '\"heritage=external-dns,external-dns/owner=default,external-dns/resource=httproute/test-metadata/test-metadata-add\"' for Azure DNS zone 'basil.sbx.org.cloud'."
time="2025-12-02T17:16:54Z" level=info msg="Updating A record named 'metadata-test' to '9.163.156.200' for Azure DNS zone 'basil.sbx.org.cloud'."
time="2025-12-02T17:16:55Z" level=info msg="Updating TXT record named 'a-metadata-test' to '\"heritage=external-dns,external-dns/owner=default,external-dns/resource=httproute/test-metadata/test-metadata-add\"' for Azure DNS zone 'basil.sbx.org.cloud'."
time="2025-12-02T17:17:54Z" level=info msg="Updating A record named 'metadata-special' to '9.163.156.200' for Azure DNS zone 'basil.sbx.org.cloud'."
time="2025-12-02T17:17:54Z" level=info msg="Updating TXT record named 'a-metadata-special' to '\"heritage=external-dns,external-dns/owner=default,external-dns/resource=httproute/test-metadata/test-metadata-special\"' for Azure DNS zone 'basil.sbx.org.cloud'."

[szuecs]

FYI: This is under discussion in gateway-api if this is what we should support or not.

[ivankatliarchuk]

It does not looks consistent with other providers like aws or cloudflare

Could we have

external-dns.alpha.kubernetes.io/azure-tags: "cost-center=12345,owner=backend-team"

Current approach will require way to many annotaions on objects, and I did not get from first look that two annotations actually represent tags. There are of course limitations on number of annotitionas and character limit on annotations values. I think we better be consistent for now.

Kubernetes has 63 characters limitation on the annotation name. Example external-dns.alpha.kubernetes.io/azure-metadata-cost-center is already 59....