[dittops]

Summary

• Add ScaleToZeroConfig to CRD for configuring scale-to-zero behavior with grace period and activation scale
• Allow maxReplicas: 0 to completely disable workloads and free resources
• Track ZeroDemandSince in status for grace period calculation
• Update algorithms (BudScaler, KPA) to respect scale-to-zero configuration
• Handle zero-pod scenarios in metrics collector

Features

• Demand-based scale-to-zero: Configure scaleToZeroConfig with grace period before scaling to 0
• Manual disable: Set maxReplicas: 0 to immediately scale to 0
• Activation scale: Configure how many replicas to wake up to from zero

Example Usage

apiVersion: scaler.bud.studio/v1alpha1
kind: BudAIScaler
spec:
  minReplicas: 0
  maxReplicas: 10
  scaleToZeroConfig:
    enabled: true
    activationScale: 2
    gracePeriod: 5m

Test plan

• Unit tests pass
• Tested maxReplicas: 0 in k3d cluster - deployment scales to 0
• Tested scale back up with minReplicas: 1

🤖 Generated with Claude Code

[gemini-code-assist]

Summary of Changes

Hello @dittops, 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 introduces comprehensive scale-to-zero functionality for the BudAIScaler. It allows users to configure demand-based scaling down to zero with a grace period, manually disable workloads by setting maxReplicas to zero, and define an activation scale for waking up from a zero-replica state. These changes enhance resource efficiency and provide greater control over workload lifecycle.

Highlights

• Scale-to-Zero Configuration: Introduced ScaleToZeroConfig in the CRD to allow detailed configuration of scale-to-zero behavior, including grace periods and activation scale.
• maxReplicas: 0 Support: Enabled the ability to set maxReplicas to 0, allowing complete disabling of workloads and freeing up resources.
• Zero Demand Tracking: Added ZeroDemandSince to the scaler's status to track when demand dropped to zero, facilitating grace period calculations.
• Algorithm Updates: Modified BudScaler and KPA algorithms to properly respect and utilize the new scale-to-zero configuration.
• Metrics Handling: Ensured that the metrics collector correctly handles scenarios where the number of pods is zero.

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[gemini-code-assist]

Code Review

This pull request implements scale-to-zero support for BudAIScaler, which is a valuable feature for resource optimization. The changes include updates to the CRD, status tracking, and scaling algorithms to handle zero-replica states. The modification in budaiscaler_controller.go correctly removes the validation that prevented maxReplicas: 0, enabling workloads to be manually disabled. However, my review identified a critical side-effect of this change: a potential division-by-zero panic in the cost metrics collection logic when a workload is scaled to zero. This must be addressed before merging.

I am having trouble creating individual review comments. Click here to see my feedback.

pkg/controller/budaiscaler/budaiscaler_controller.go (206-208)

While removing this validation is necessary to support maxReplicas: 0, it introduces a critical risk of a division-by-zero panic.

The collectCostMetrics function in pkg/controller/budaiscaler/autoscaler.go calculates perReplicaCost by dividing by currentReplicas. When a workload is scaled to zero as a result of this change, currentReplicas will be 0, causing the controller to panic.

This affects both the logging statement and the returned CostMetrics struct. You should add a check to handle the currentReplicas == 0 case.

Recommendation:
In pkg/controller/budaiscaler/autoscaler.go, update collectCostMetrics to safely handle zero replicas:

// in collectCostMetrics function
var perReplicaCost float64
if currentReplicas > 0 {
	perReplicaCost = hourlyCost / float64(currentReplicas)
}

klog.V(4).InfoS("Cost metrics calculated",
	"provider", provider,
	"replicas", currentReplicas,
	"hourlyCost", hourlyCost,
	"budgetPerHour", budgetPerHour,
	"perReplicaCost", perReplicaCost)

return &types.CostMetrics{
	CurrentCostPerHour:    hourlyCost,
	BudgetPerHour:         budgetPerHour,
	PerReplicaCostPerHour: perReplicaCost,
}