Fix Kubeconfig getting uploaded to cluster despite remote_identity: SERVICE_ACCOUNT

[romilbhardwaj]

Kubeconfig was being uploaded to Kubernetes pods even when the default remote_identity: SERVICE_ACCOUNT was set. remote_identity: SERVICE_ACCOUNT should never upload the kubeconfig.

Turns out this was because SSH inherits from Kubernetes and we effectively select the kubeconfig in get_cloud_credential_file_mounts. I.e., when collecting credentials to upload:

• Kubernetes was correctly excluded
• SSH was not excluded
• SSH.get_credential_file_mounts() ended up uploading kubeconfig

Also added tests to prevent this regression in the future.

[gemini-code-assist]

Summary of Changes

Hello @romilbhardwaj, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical security and configuration issue where Kubernetes kubeconfig files were being uploaded to pods even when remote_identity: SERVICE_ACCOUNT was specified, which should prevent such uploads. The fix involves refining the cloud credential exclusion logic to correctly identify and prevent kubeconfig uploads via SSH, which inherits Kubernetes' credential handling. Comprehensive tests have been added to validate this fix and safeguard against future recurrences.

Highlights

• Kubeconfig Upload Fix: Resolved an issue where the Kubeconfig file was inadvertently uploaded to Kubernetes pods, even when remote_identity: SERVICE_ACCOUNT was configured. This occurred because SSH, inheriting from Kubernetes, was not explicitly excluded during credential collection, leading to its get_credential_file_mounts() method uploading the kubeconfig.
• Explicit Cloud Exclusion: Modified the write_cluster_config function in sky/backends/backend_utils.py to explicitly exclude both Kubernetes and SSH clouds when allowed_contexts is None, ensuring that the kubeconfig is not uploaded in scenarios where it shouldn't be.
• Regression Prevention Tests: Added new unit tests to tests/unit_tests/test_backend_utils.py to specifically cover the scenario where both Kubernetes and SSH clouds are excluded, and a regression test demonstrating the previous buggy behavior, preventing future recurrences of this kubeconfig upload issue.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a bug where the kubeconfig was being uploaded incorrectly for Kubernetes clusters with remote_identity: SERVICE_ACCOUNT. The fix to explicitly exclude both Kubernetes and SSH clouds is appropriate given the inheritance relationship. The added tests validate the fix, but I've suggested a refactoring to make them clearer and more robust by combining them into a single, more explicit test case. Overall, this is a good change that addresses a subtle but important issue.