starlark: Inject Sidecar #

Overview #

In this example, we are going to demonstrate how to declaratively run the starlark function with an inline starlark script as function configuration to inject sidecar container to Deployment.

Fetch the example package #

Get the example package by running the following commands:

$ kpt pkg get https://github.com/kptdev/krm-functions-catalog/tree/master/examples/starlark-inject-sidecar

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

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: inject-sidecar-to-depl
source: |
  def ensure_inject_sidecar_to_depl(r):
    if r["apiVersion"] == "apps/v1" and r["kind"] == "Deployment":
      containers = r["spec"]["template"]["spec"]["containers"]
      for container in containers:
        if container["name"] == "logging-agent":
          return
      sidecar = {
        "name": "logging-agent",
        "image": "k8s.gcr.io/fluentd-gcp:1.30",
      }
      containers.append(sidecar)
  def ensure_inject_sidecar(resources):
    for resource in resources:
      ensure_inject_sidecar_to_depl(resource)
  ensure_inject_sidecar(ctx.resource_list["items"])

The Starlark script is embedded in the source field. This script reads the input KRM resources from ctx.resource_list and inject a logging agent sidecar container in the Deployment.

Function invocation #

Invoke the function by running the following commands:

$ kpt fn render starlark-inject-sidecar

Expected result #

The logging agent container should have been injected.