Backend traffic distribution fixes

[ymesika]

Description

The BackendObjectIR.Equals() method was missing comparison of the TrafficDistribution field, so backends with different traffic distribution values (like "Any" vs "PreferNetwork") were incorrectly considered equal. This could lead to stale configurations being reused when traffic distribution policies changed. The fix adds c.TrafficDistribution == in.TrafficDistribution to the equality check.

Also changed PreferSameNetwork to PreferNetwork as this is the expected value from Istio upstream. There is no constant for that there.

Fixes #13004

Change Type

/kind fix

Changelog

Fixed issue with stale configuration when changing a service traffic distribution.

Additional Notes

[Copilot]

Pull request overview

This PR fixes a critical bug where the TrafficDistribution field was not being compared in the Equals() methods of BackendObjectIR and EndpointsForBackend. This caused backends with different traffic distribution policies (e.g., "Any" vs "PreferNetwork") to be incorrectly treated as equal, leading to stale configurations when traffic distribution changed. Additionally, the PR renames the traffic distribution value from PreferSameNetwork to PreferNetwork to align with Istio's upstream naming convention.

Key changes:

• Added TrafficDistribution comparison to BackendObjectIR.Equals() and EndpointsForBackend.Equals() methods
• Added TrafficDistribution field to EndpointsForBackend.EmptyCopy() method
• Renamed TrafficDistributionPreferSameNetwork constant to TrafficDistributionPreferNetwork
• Updated all references throughout the codebase to use PreferNetwork instead of PreferSameNetwork

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pkg/pluginsdk/ir/model.go	Added TrafficDistribution to EmptyCopy() and Equals() methods for EndpointsForBackend; removed TODO comment
pkg/pluginsdk/ir/backend.go	Added TrafficDistribution comparison to BackendObjectIR.Equals() method; removed TODO comment
pkg/pluginsdk/ir/backend_test.go	Added comprehensive unit tests for BackendObjectIR.Equals() covering various traffic distribution scenarios
internal/kgateway/wellknown/traffic_dist.go	Renamed constant and updated parsing logic from PreferSameNetwork to PreferNetwork
internal/kgateway/setup/testdata/traffic_distribution/svc-prefer-same-network.yaml	Updated annotation value from PreferSameNetwork to PreferNetwork
internal/kgateway/setup/testdata/traffic_distribution/se-prefer-same-network.yaml	Updated annotation values and comments from PreferSameNetwork to PreferNetwork
internal/kgateway/krtcollections/endpoints_test.go	Updated test to use renamed TrafficDistributionPreferNetwork constant
internal/kgateway/endpoints/prioritize.go	Updated case statement to use renamed TrafficDistributionPreferNetwork constant

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[Copilot]

The new test TestBackendObjectIREquals doesn't test scenarios where other fields differ (e.g., different Port, Namespace, or Name). While testing TrafficDistribution is good, consider adding test cases that verify the method correctly handles differences in other key fields to ensure comprehensive coverage of the equality logic.

[Copilot]

While EndpointsForBackend.Equals() now correctly compares TrafficDistribution, there are no unit tests that directly verify the Equals() method behavior with different TrafficDistribution values. The existing test TestEndpointsForUpstreamWithDifferentTrafficDistributionButSameEndpoints only verifies hash differences. Consider adding a test similar to TestBackendObjectIREquals that directly calls EndpointsForBackend.Equals() with different traffic distributions to ensure the equality logic is properly validated.