feat: add CEL metrics tracking for expression evaluations

[govindup63]

This PR implements CEL expression evaluation cost tracking and exposes metrics in the ResourceGroup instance status, addressing issue #190.

The implementation tracks the cost of all CEL expression evaluations during reconciliation and provides both total cost and per-resource cost breakdown in the instance status. This enables platform teams to monitor and optimize CEL expression performance.

Changes

Core Implementation

• Added CEL metrics tracking in pkg/runtime/runtime.go:

  • CELMetrics struct to track total cost and per-resource costs
  • RecordCELCost() method to accumulate costs during expression evaluation
  • GetCELMetrics() method that returns a deep copy to protect internal state
  • ResetCELMetrics() method for resetting metrics (interface compliance)
  • Cost tracking integrated into all CEL evaluation points:
    • Static variable evaluation (evaluateStaticVariables)
    • Dynamic variable evaluation (evaluateDynamicVariables)
    • includeWhen expressions (ReadyToProcessResource)
    • readyWhen expressions (IsResourceReady)

• Status exposure in pkg/controller/instance/controller_status.go:

  • Added celMetrics to instance status with totalCost and costPerResource
  • Added nil checks for safety when runtime creation fails

• CRD schema updates in pkg/graph/crd/:

  • Added celMetrics as a default status field in CRD schema
  • Defined proper schema structure for totalCost (int64) and costPerResource (map[string]int64)
  • Added additionalProperties: true to status schema to support controller-injected fields

Testing

• Added comprehensive unit tests in pkg/runtime/runtime_test.go:
  • TestCELMetrics - tests cost accumulation, retrieval, and reset
  • TestEvaluateExpressionCostTracking - verifies cost tracking is enabled
  • TestRuntimeCELCostIntegration - integration test for static variable cost tracking
  • TestIsResourceReadyCostTracking - tests readyWhen expression cost tracking
  • TestReadyToProcessResourceCostTracking - tests includeWhen expression cost tracking
  • TestCELCostMultipleResources - tests cost tracking across multiple resources
  • TestCELCostReadyWhen - focused test for readyWhen expressions

Example Output

After reconciliation, the instance status includes CEL metrics:

apiVersion: kro.run/v1alpha1
kind: WebApp
metadata:
  name: my-application
spec:
  # ... spec fields
status:
  celMetrics:
    totalCost: 76
    costPerResource:
      schema: 18        # Static variable evaluations
      deployment: 14    # Deployment resource expressions
      service: 22       # Service resource expressions
      ingress: 16       # Ingress includeWhen evaluation
      instance: 6       # Instance variable evaluations
  # ... other status fields

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: govindup63
Once this PR has been reviewed and has the lgtm label, please assign barney-s for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[k8s-ci-robot]

Hi @govindup63. Thanks for your PR.

I'm waiting for a github.com member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[bschaatsbergen]

Hey @govindup63, thanks for working on this! It would be good to align with @TusharMohapatra07 in #931, since they're doing similar work.

[k8s-ci-robot]

PR needs rebase.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[TusharMohapatra07]

Hey @govindup63, thanks for working on this! It would be good to align with @TusharMohapatra07 in #931, since they're doing similar work.

Hey @bschaatsbergen! Hope you're doing great :)
could you please elaborate on the next steps ?

[govindup63]

Hi @a-hilaly , just a gentle ping on this PR when you get a chance.
Would really appreciate your review. Thanks!

[a-hilaly]

thanks for working on this.

I’m going to close this PR for now. Exposing CEL evaluation cost in instance status adds a new public status surface, and I don’t think we have the design fully settled yet for what exactly should be tracked, how stable that contract should be, and whether this belongs in status vs other observability paths.

/close

[k8s-ci-robot]

@a-hilaly: Closed this PR.

Details

In response to this:

thanks for working on this.

I’m going to close this PR for now. Exposing CEL evaluation cost in instance status adds a new public status surface, and I don’t think we have the design fully settled yet for what exactly should be tracked, how stable that contract should be, and whether this belongs in status vs other observability paths.

/close

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.