hpa-primitive

HPA Primitive Example

This example demonstrates the usage of the hpa primitive within the operator component framework. It shows how to manage a Kubernetes HorizontalPodAutoscaler as a component of a larger application, utilizing features like:

• Base Construction: Initializing an HPA with a scale target ref, min/max replicas, and labels.
• Feature Mutations: Applying version-gated or conditional changes (CPU metrics, memory metrics, scaling behavior) using the Mutator.
• Operational Status: Reporting HPA health based on ScalingActive and AbleToScale conditions.
• Suspension (Delete): Demonstrating delete-on-suspend behavior — the HPA is removed during suspension to prevent it from scaling the target back up.
• Data Extraction: Harvesting information from the reconciled resource.

Directory Structure

• app/: Defines the mock ExampleApp CRD and the controller that uses the component framework.
• features/: Contains modular feature definitions:
  • mutations.go: CPU metric, memory metric, and scale behavior feature mutations.
• resources/: Contains the central NewHPAResource factory that assembles all features using the hpa.Builder.
• main.go: A standalone entry point that demonstrates a reconciliation loop using a fake client.

Running the Example

You can run this example directly using go run:

go run examples/hpa-primitive/main.go

This will:

1. Initialize a fake Kubernetes client.
2. Create an ExampleApp owner object.
3. Reconcile the ExampleApp components through multiple spec changes.
4. Print the resulting status conditions and HPA state.