starlark: PodDisruptionBudget #

Overview #

In this example, we are going to demonstrate how to declaratively run the starlark function with StarlarkRun as the functionConfig. And we will show how to access a parameter with complex data structure in the functionConfig and use it in the script.

Fetch the example package #

Get the example package by running the following commands:

$ kpt pkg get https://github.com/kptdev/krm-functions-catalog.git/examples/starlark-poddisruptionbudget

We are going to use the following Kptfile and fn-config.yaml to configure the function:

# Kptfile
apiVersion: kpt.dev/v1
kind: Kptfile
metadata:
  name: example
pipeline:
  mutators:
    - image: ghcr.io/kptdev/krm-functions-catalog/starlark:latest
      configPath: fn-config.yaml

# fn-config.yaml
apiVersion: fn.kpt.dev/v1alpha1
kind: StarlarkRun
metadata:
  name: pdb-for-depl
params:
  pdb:
    apiVersion: policy/v1beta1
    kind: PodDisruptionBudget
    metadata:
      name: nginx-pdb
    spec:
      selector:
        matchLabels:
          app: nginx
      minAvailable: 1
source: |
  def is_pdb(r):
    return r["apiVersion"] == "policy/v1beta1" and r["kind"] == "PodDisruptionBudget" and r["metadata"]["name"] == "nginx-pdb"
  def ensure_pdb(resources, pdb):
    for resource in resources:
      if is_pdb(resource):
        return
    resources.append(pdb)
  pdb = ctx.resource_list["functionConfig"]["params"]["pdb"]
  ensure_pdb(ctx.resource_list["items"], pdb)

The Starlark script lives in the source field. This script reads the input resources from ctx.resource_list and the PodDisruptionBudget resource from ctx.resource_list["functionConfig"]["params"]["pdb"]. It will ensure there is a PodDisruptionBudget resource for the nginx Deployment. If not, it will create it with the PodDisruptionBudget resource provided in params.

Function invocation #

Invoke the function by running the following commands:

$ kpt fn render starlark-poddisruptionbudget

Expected result #

A new file should have been created, and it should contain a PodDisruptionBudget object.