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py-custom-metrics

Code Quality

Kubernetes custom metrics plumbing for Python

Architecture

This code includes a Flask API which implements the Kubernetes Custom Metrics API which is described in detail here.

The three major routes that you may wish to implement are:

  • namespace: Get metrics on a Namespace.
  • cluster_objects: Get metrics for one or more cluster-scoped objects, by name or label selector.
  • namespaced_objects: Get metrics for one or more namespace-scoped objects, by name or label selector.

For instance, a Horizontal Pod Autoscaler (HPA) v2 configured for a Deployment with the following metrics will query the namespaced_objects endpoint for the foo metric with the label selector defined in the Deployment.

  - type: Pods
    pods:
      metric:
        name: foo
      target:
        averageValue: 50
        type: "AverageValue"

All three routes should return a MetricValueList, which is defined in this proto file. This is reimplemented with dataclasses here.

The application is installed as a Deployment and Service in the custom-metrics Namespace. It serves a self-signed certificate. The API is registered with Kubernetes using an APIService which includes the signing CA bundle for TLS authentication.

Kubernetes will query the root API path, as well as for an OpenAPI specification (unimplemented). If the root path query is successful, the API registration will complete and Kubernetes will begin aggregating these API endpoints.

Development

For easy development, run scripts/develop.sh. This will configure Kubernetes (tested in Kind) to query your host machine on 8443, and start Flask in development mode on the same port (with live-reloading).

As a smoke test, you may wish to run scripts/test.sh which will query for the metric metric_name on the default namespace.

Deployment

Once you have finished development, the script scripts/deploy.sh will deploy the code to run in Kubernetes with a more secure TLS configuration. If your code can run in a distributed manner (there is no shared state), you may wish to increase the number of replicas of this Deployment.

Removal

Run scripts/remove.sh to reverse scripts/deploy.sh.