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

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: vaspoz / name: Basil Pozdeev (0d0f4c5, 1628f16, 212f7db, 83edb29, 9e08a42)

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[vflaux]

/ok-to-test

[coveralls]

Pull Request Test Coverage Report for Build 20573485375

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 39 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 78.96%

---

Files with Coverage Reduction	New Missed Lines	%
azure/azure.go	39	81.36%

Totals
Change from base Build 20569555245:	0.04%
Covered Lines:	16028
Relevant Lines:	20299

---

💛 - 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.

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[vaspoz]

/retest

[vaspoz]

/retest

[ivankatliarchuk]

/lgtm

[mloiseleur]

There is the exact same func for (at least) cloudflare:

external-dns/provider/cloudflare/cloudflare.go

Lines 732 to 743 in 02abd24

	func parseTagsAnnotation(tagString string) []string {
	tags := strings.Split(tagString, ",")
	cleanedTags := make([]string, 0, len(tags))
	for _, tag := range tags {
	trimmed := strings.TrimSpace(tag)
	if trimmed != "" {
	cleanedTags = append(cleanedTags, trimmed)
	}
	}
	sort.Strings(cleanedTags)
	return cleanedTags
	}

🤔 Wdyt about moving it to source/annotations and use it in both ?

[k8s-ci-robot]

New changes are detected. LGTM label has been removed.