KCL is a constraint-based record & functional domain language. Full documents of KCL can be found here.

You can use the Helm-KCL-Plugin to

• Edit the helm charts in a hook way to separate data and logic for the Kubernetes manifests management.
• For multi-environment and multi-tenant scenarios, you can maintain these configurations gracefully rather than simply copy and paste.
• Validate all KRM resources using the KCL schema.

helm plugin install https://github.com/kcl-lang/helm-kcl

Pick a release tarball from the releases page.

Unpack the tarball in your helm plugins directory ($(helm home)/plugins).

E.g.

curl -L $TARBALL_URL | tar -C $(helm home)/plugins -xzv

• GoLang 1.23

Make sure you do not have a version of helm-kcl installed. You can remove it by running the command.

helm plugin uninstall kcl

The first step is to download the repository and enter the directory. You can do this via git clone or downloading and extracting the release. If you clone via git, remember to check out the latest tag for the latest release.

Next, depending on which helm version you have, install the plugin into helm.

make install

make install/helm3

helm kcl template --file ./examples/workload-charts-with-kcl/kcl-run.yaml

The content of kcl-run.yaml looks like this:

# kcl-config.yaml
apiVersion: krm.kcl.dev/v1alpha1
kind: KCLRun
metadata:
  name: set-annotation
spec:
  # EDIT THE SOURCE!
  # This should be your KCL code which preloads the `ResourceList` to `option("items")
  source: |
    [resource | {if resource.kind == "Deployment": metadata.annotations: {"managed-by" = "helm-kcl-plugin"}} for resource in option("items")]

repositories:
  - name: workload
    path: ./workload-charts

The output is:

apiVersion: v1
kind: Service
metadata:
  labels:
    app.kubernetes.io/instance: workload
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/name: workload
    app.kubernetes.io/version: 0.1.0
    helm.sh/chart: workload-0.1.0
  name: workload
spec:
  ports:
  - name: www
    port: 80
    protocol: TCP
    targetPort: 80
  selector:
    app.kubernetes.io/instance: workload
    app.kubernetes.io/name: workload
  type: ClusterIP
---
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app.kubernetes.io/instance: workload
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/name: workload
    app.kubernetes.io/version: 0.1.0
    helm.sh/chart: workload-0.1.0
  name: workload
  annotations:
    managed-by: helm-kcl-plugin
spec:
  selector:
    matchLabels:
      app.kubernetes.io/instance: workload
      app.kubernetes.io/name: workload
  template:
    metadata:
      labels:
        app.kubernetes.io/instance: workload
        app.kubernetes.io/name: workload
    spec:
      containers:
      - image: "nginx:alpine"
        name: frontend

• GoLang 1.23

git clone https://github.com/kcl-lang/helm-kcl.git
cd helm-kcl
go run main.go

go test -v ./...

You need to put your KCL script source in the functionConfig of kind KCLRun and then the function will run the KCL script that you provide.

# Verify that the annotation is added to the `Deployment` resource and the other resource `Service` 
# does not have this annotation.
diff \
  <(helm template ./examples/workload-charts-with-kcl/workload-charts) \
  <(go run main.go template --file ./examples/workload-charts-with-kcl/kcl-run.yaml) |\
  grep annotations -A1

The output is

>   annotations:
>     managed-by: helm-kcl-plugin

Bump version in plugin.yaml:

code plugin.yaml
git commit -m 'Bump helm-kcl version to 0.x.y'

Set GITHUB_TOKEN and run:

make docker-run-release

Here's what you can do in the KCL script:

• Read resources from option("items"). The option("items") complies with the KRM Functions Specification.
• Return a KPM list for output resources.
• Return an error using assert {condition}, {error_message}.
• Read the environment variables. e.g. option("PATH") (Not yet implemented).
• Read the OpenAPI schema. e.g. option("open_api")["definitions"]["io.k8s.api.apps.v1.Deployment"] (Not yet implemented).

Full documents of KCL can be found here.

See here for more examples.

• helmfile
• helm-diff
• helm-secrets
• helm-s3
• helm-git