fix: remove unused LocalDNS health check domain

[Saewon Kwak (saewoni)]

Description

Remove the unused domain option from LocalDNS CoreDNS forward health check configuration. The LocalDNS health-check scope is intentionally limited to the currently supported knobs:

• duration
• no_rec
• failfast_all_unhealthy_upstreams

The removed proto field number/name are reserved so they are not reused accidentally. This keeps AgentBaker aligned with the aks-rp HCP proto cleanup and avoids exposing a health-check FQDN knob that aks-rp does not support end-to-end today.

Testing

• cd aks-node-controller && go test ./parser ./pkg/nodeconfigutils
• go test ./pkg/agent ./pkg/agent/datamodel

Related

• aks-rp HCP proto cleanup: PR 16851658
• aks-rp LocalDNS wiring: PR 16788351

[Copilot]

Pull request overview

This PR removes the unused LocalDNS forward health-check domain knob end-to-end (AgentBaker datamodel + rendering templates + aks-node-controller proto), keeping the health-check surface limited to the supported options and preventing accidental reuse of the removed protobuf field.

Changes:

• Removed domain from LocalDNSHealthCheck in the AgentBaker datamodel and from the CoreDNS Corefile/template rendering paths.
• Updated unit tests to assert the generated Corefile no longer contains any domain directive for health checks.
• Reserved protobuf field number/name (3 / "domain") in LocalDnsHealthCheck to preserve wire-compatibility expectations and avoid reuse.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pkg/agent/datamodel/types.go	Drops Domain field and getter from LocalDNSHealthCheck.
pkg/agent/baker.go	Removes rendering of domain from LocalDNS forward health_check template blocks.
pkg/agent/baker_test.go	Updates expectations to validate Corefile contains only supported health-check knobs.
aks-node-controller/proto/aksnodeconfig/v1/localdns_config.proto	Reserves protobuf field number/name for removed domain field.
aks-node-controller/pkg/gen/aksnodeconfig/v1/localdns_config.pb.go	Regenerated output reflecting reserved field and removed accessor/field.
aks-node-controller/parser/templates/localdns.toml.gtpl	Removes template emission of domain for health_check.
aks-node-controller/parser/helper_test.go	Removes domain-related test cases and tightens “no domain emitted” assertions.

Files not reviewed (1)

• aks-node-controller/pkg/gen/aksnodeconfig/v1/localdns_config.pb.go: Generated file

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