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Helmfile KCL Plugin

Introduction​

Helmfile is a declarative spec for deploying helm charts. It lets you...

  • Keep a directory of chart value files and maintain changes in version control.
  • Apply CI/CD to configuration changes.
  • Periodically sync to avoid skew in environments.

KCL can be used to create functions to mutate and/or validate the YAML Kubernetes Resource Model (KRM) input/output format, and we provide Kustomize KCL functions to simplify the function authoring process.

Prerequisites​

  • Install helmfile
  • Prepare a Kubernetes cluster

Quick Start​

Let’s write a KCL function which add annotation managed-by=helmfile-kcl only to Deployment resources.

1. Get the Example​

git clone https://github.com/kcl-lang/helmfile-kcl.git
cd ./helmfile-kcl/examples/hello-world/

We can execute the command to show config

cat helmfile.yaml

The output is

repositories:
  - name: prometheus-community
    url: https://prometheus-community.github.io/helm-charts

releases:
  - name: prom-norbac-ubuntu
    namespace: prometheus
    chart: prometheus-community/prometheus
    set:
      - name: rbac.create
        value: false
    transformers:
      # Use KCL Plugin to mutate or validate Kubernetes manifests.
      - apiVersion: krm.kcl.dev/v1alpha1
        kind: KCLRun
        metadata:
          name: "set-annotation"
          annotations:
            config.kubernetes.io/function: |
              container:
                image: docker.io/kcllang/kustomize-kcl:v0.2.0
        spec:
          source: |
            [resource | {if resource.kind == "Deployment": metadata.annotations: {"managed-by" = "helmfile-kcl"}} for resource in option("resource_list").items]

In the above config, we use a KCLRun plugin to assign the transfomer field. This means that we will add annotations to all deployment resources in the prometheus helm chart.

2. Test and Run​

Firstly, init the helmfile tool.

helmfile init

The output may looks like this:

The helm plugin helm-git is not installed, do you need to install it [y/n]: y
Install helm plugin helm-git
Installed plugin: helm-git

helmfile initialization completed!
...

Then apply the configuration.

helmfile apply

The output is

Adding repo prometheus-community https://prometheus-community.github.io/helm-charts
"prometheus-community" has been added to your repositories

...

Guides for Developing KCL​

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

  • Read resources from option("items"). The option("items") complies with the KRM Functions Specification.
  • Return a KRM list for output resources.
  • Return an error using assert {condition}, {error_message}.
  • Read the PATH variables. e.g. option("PATH").
  • Read the environment variables. e.g. option("env").

More Documents and Examples​