feat: support kubernetes.io/ingress.class annotations

[ronething]

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches
• Documentation
• Refactor
• Chore
• CI/CD or Tests

What this PR does / why we need it:

add support for ingress annotations: kubernetes.io/ingress.class.

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[github-actions]

conformance test report - apisix-standalone mode

apiVersion: gateway.networking.k8s.io/v1
date: "2025-10-21T08:03:22Z"
gatewayAPIChannel: experimental
gatewayAPIVersion: v1.3.0
implementation:
  contact: null
  organization: APISIX
  project: apisix-ingress-controller
  url: https://github.com/apache/apisix-ingress-controller.git
  version: v2.0.0
kind: ConformanceReport
mode: default
profiles:
- core:
    result: success
    statistics:
      Failed: 0
      Passed: 12
      Skipped: 0
  name: GATEWAY-GRPC
  summary: Core tests succeeded.
- core:
    result: partial
    skippedTests:
    - HTTPRouteHTTPSListener
    statistics:
      Failed: 0
      Passed: 32
      Skipped: 1
  extended:
    result: partial
    skippedTests:
    - HTTPRouteRedirectPortAndScheme
    statistics:
      Failed: 0
      Passed: 8
      Skipped: 1
    supportedFeatures:
    - GatewayAddressEmpty
    - GatewayPort8080
    - HTTPRouteDestinationPortMatching
    - HTTPRouteHostRewrite
    - HTTPRouteMethodMatching
    - HTTPRoutePortRedirect
    - HTTPRouteRequestMirror
    - HTTPRouteResponseHeaderModification
    - HTTPRouteSchemeRedirect
    unsupportedFeatures:
    - GatewayHTTPListenerIsolation
    - GatewayInfrastructurePropagation
    - GatewayStaticAddresses
    - HTTPRouteBackendProtocolH2C
    - HTTPRouteBackendProtocolWebSocket
    - HTTPRouteBackendRequestHeaderModification
    - HTTPRouteBackendTimeout
    - HTTPRouteParentRefPort
    - HTTPRoutePathRedirect
    - HTTPRoutePathRewrite
    - HTTPRouteQueryParamMatching
    - HTTPRouteRequestMultipleMirrors
    - HTTPRouteRequestPercentageMirror
    - HTTPRouteRequestTimeout
  name: GATEWAY-HTTP
  summary: Core tests partially succeeded with 1 test skips. Extended tests partially
    succeeded with 1 test skips.

[github-actions]

conformance test report - apisix mode

apiVersion: gateway.networking.k8s.io/v1
date: "2025-10-21T08:03:34Z"
gatewayAPIChannel: experimental
gatewayAPIVersion: v1.3.0
implementation:
  contact: null
  organization: APISIX
  project: apisix-ingress-controller
  url: https://github.com/apache/apisix-ingress-controller.git
  version: v2.0.0
kind: ConformanceReport
mode: default
profiles:
- core:
    result: success
    statistics:
      Failed: 0
      Passed: 12
      Skipped: 0
  name: GATEWAY-GRPC
  summary: Core tests succeeded.
- core:
    failedTests:
    - HTTPRouteInvalidBackendRefUnknownKind
    result: failure
    skippedTests:
    - HTTPRouteHTTPSListener
    statistics:
      Failed: 1
      Passed: 31
      Skipped: 1
  extended:
    result: partial
    skippedTests:
    - HTTPRouteRedirectPortAndScheme
    statistics:
      Failed: 0
      Passed: 8
      Skipped: 1
    supportedFeatures:
    - GatewayAddressEmpty
    - GatewayPort8080
    - HTTPRouteDestinationPortMatching
    - HTTPRouteHostRewrite
    - HTTPRouteMethodMatching
    - HTTPRoutePortRedirect
    - HTTPRouteRequestMirror
    - HTTPRouteResponseHeaderModification
    - HTTPRouteSchemeRedirect
    unsupportedFeatures:
    - GatewayHTTPListenerIsolation
    - GatewayInfrastructurePropagation
    - GatewayStaticAddresses
    - HTTPRouteBackendProtocolH2C
    - HTTPRouteBackendProtocolWebSocket
    - HTTPRouteBackendRequestHeaderModification
    - HTTPRouteBackendTimeout
    - HTTPRouteParentRefPort
    - HTTPRoutePathRedirect
    - HTTPRoutePathRewrite
    - HTTPRouteQueryParamMatching
    - HTTPRouteRequestMultipleMirrors
    - HTTPRouteRequestPercentageMirror
    - HTTPRouteRequestTimeout
  name: GATEWAY-HTTP
  summary: Core tests failed with 1 test failures. Extended tests partially succeeded
    with 1 test skips.

[github-actions]

conformance test report

apiVersion: gateway.networking.k8s.io/v1
date: "2025-10-21T08:11:26Z"
gatewayAPIChannel: experimental
gatewayAPIVersion: v1.3.0
implementation:
  contact: null
  organization: APISIX
  project: apisix-ingress-controller
  url: https://github.com/apache/apisix-ingress-controller.git
  version: v2.0.0
kind: ConformanceReport
mode: default
profiles:
- core:
    failedTests:
    - GRPCExactMethodMatching
    - GRPCRouteHeaderMatching
    - GRPCRouteListenerHostnameMatching
    result: failure
    statistics:
      Failed: 3
      Passed: 9
      Skipped: 0
  name: GATEWAY-GRPC
  summary: Core tests failed with 3 test failures.
- core:
    failedTests:
    - GatewayWithAttachedRoutes
    result: failure
    skippedTests:
    - HTTPRouteHTTPSListener
    statistics:
      Failed: 1
      Passed: 31
      Skipped: 1
  extended:
    result: partial
    skippedTests:
    - HTTPRouteRedirectPortAndScheme
    statistics:
      Failed: 0
      Passed: 8
      Skipped: 1
    supportedFeatures:
    - GatewayAddressEmpty
    - GatewayPort8080
    - HTTPRouteDestinationPortMatching
    - HTTPRouteHostRewrite
    - HTTPRouteMethodMatching
    - HTTPRoutePortRedirect
    - HTTPRouteRequestMirror
    - HTTPRouteResponseHeaderModification
    - HTTPRouteSchemeRedirect
    unsupportedFeatures:
    - GatewayHTTPListenerIsolation
    - GatewayInfrastructurePropagation
    - GatewayStaticAddresses
    - HTTPRouteBackendProtocolH2C
    - HTTPRouteBackendProtocolWebSocket
    - HTTPRouteBackendRequestHeaderModification
    - HTTPRouteBackendTimeout
    - HTTPRouteParentRefPort
    - HTTPRoutePathRedirect
    - HTTPRoutePathRewrite
    - HTTPRouteQueryParamMatching
    - HTTPRouteRequestMultipleMirrors
    - HTTPRouteRequestPercentageMirror
    - HTTPRouteRequestTimeout
  name: GATEWAY-HTTP
  summary: Core tests failed with 1 test failures. Extended tests partially succeeded
    with 1 test skips.

[Copilot]

Pull Request Overview

This PR adds support for the deprecated kubernetes.io/ingress.class annotation as a fallback mechanism for specifying ingress class. The implementation ensures backward compatibility by prioritizing the spec.ingressClassName field while falling back to the annotation when the spec field is not set.

Key changes:

• Modified ingress class extraction logic to check annotation when spec field is empty
• Updated indexing and reconciliation logic to handle annotation-based class specification
• Added E2E test to verify annotation-based ingress class functionality

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
internal/controller/utils.go	Adds constant for annotation key and implements fallback logic in ExtractIngressClass
internal/controller/ingress_controller.go	Updates reconciler to handle both spec-based and annotation-based class names
internal/controller/indexer/indexer.go	Modifies indexing function to index ingresses by annotation-based class name
test/e2e/ingress/ingress.go	Adds E2E test case validating annotation-based ingress class functionality

---

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[Copilot]

The constant ingressClassNameAnnotation is duplicated across multiple files (utils.go, ingress_controller.go, and indexer.go). Consider defining it once in a shared constants file to avoid inconsistencies and improve maintainability.

Suggested change

	const (
	ingressClassNameAnnotation = "kubernetes.io/ingress.class"
	)
	// Use shared constant from internal/utils instead of local definition.