khelm

A Helm chart templating CLI, helm to kustomize converter, kpt function and kustomize plugin.

Formerly known as "helm-kustomize-plugin".

Motivation / History

Helm charts provide a great way to share and reuse Kubernetes applications and there is a lot of them. However writing helm templates is cumbersome and you cannot reuse a chart properly if it does not yet support a particular parameter/value.

Kustomize solves these issues declaratively by merging Kubernetes API objects which grants users of a kustomization the freedom to change anything. However kustomize neither supports lifecycle management nor templating with externally passed in values (which is sometimes still required).

To overcome the gap between helm and kustomize initially this repository provided a kustomize plugin and k8spkg was used for lifecycle management.
Since kpt is published helm and kustomize can be run as (chained) kpt functions supporting declarative, GitOps-based workflows. kpt also supports dynamic modification of static (rendered) manifests with externally passed in values using setters as well as dependency and lifecycle management.

Features

• Templates/renders a Helm chart
• Builds local charts automatically when templating
• Automatically fetches and updates required repository index files when needed
• Allows to automatically reload dependencies when lock file is out of sync
• Allows to use any repository without registering it in repositories.yaml
• Allows to exclude certain resources from the Helm chart output
• Allows to enforce namespace-scoped resources within the template output
• Allows to enforce a namespace on all resources
• Allows to convert a chart's output into a kustomization

Supported interfaces

khelm can be used as:

• kpt function
• kustomize exec plugin
• kustomize Containerized KRM Function
• CLI
• Go API

Usage examples can be found in the example and e2e directories.

kpt function

khelm can be used as a containerized KRM function with kpt. The khelm function templates a chart and returns the output as single manifest file or kustomization directory (when outputPath ends with /) that kpt writes to disk.

In opposite to the kustomize plugin approach, kpt function outputs can be audited reliably when committed to a git repository, a kpt function does not depend on particular plugin binaries on the host and CD pipelines can run without dependencies to rendering technologies and chart servers since they just apply static manifests to a cluster (e.g. using kpt live apply).

kpt function usage example

When using the khelm image directly with kpt, it must be invoked as an imperative function since it requires a chart to be mounted or network access to fetch a chart. This is shown as follows:

cat - > fn-config.yaml <<-EOF
  apiVersion: khelm.mgoltzsche.github.com/v2
  kind: ChartRenderer
  metadata:
    name: cert-manager-manifest-generator-config
  repository: https://charts.jetstack.io
  chart: cert-manager
  version: 0.9.x
  name: myrelease
  namespace: cert-manager
  values:
    webhook:
      enabled: false
  outputPath: output-manifest.yaml
EOF
kpt fn eval --image mgoltzsche/khelm:latest --fn-config fn-config.yaml --network .

For all available fields see the table below.

To use a local chart or values file, the source must be mounted to the function container using e.g. kpt fn eval --mount="type=bind,src=$(pwd),dst=/source,rw=true" --image mgoltzsche/khelm --fn-config fn-config.yaml ..
The kpt examples and corresponding e2e tests show how to do that.

To use khelm as a declarative function, you could distribute a container image that includes both khelm and your chart as shown in the declarative example.

kpt can also be leveraged to sync charts from other git repositories into your own repository using the kpt pkg get and kpt pkg update commands (with a corresponding dependency set up) before running the khelm function.

Caching Helm Charts and repository index files

When external Helm Charts are used the download of their repositories' index files and of the charts itself can take a significant amount of time that adds up when running multiple functions or calling a function frequently during development.
To speed this up caching can be enabled by mounting a host directory into the container at /helm, e.g. kpt fn run --mount "type=bind,src=$HOME/.khelm,dst=/helm,rw=true" .. Please be aware that the presence of /helm/repository/repositories.yaml enables a strict repository policy by default (see repository configuration). Therefore, to be independent of existing Helm 2 installations, a host's ~/.helm directory should not be mounted to /helm in most cases but the ~/.helm/cache subdirectory into /helm/cache.

kustomize exec plugin

khelm can be used as kustomize exec plugin. Though plugin support in kustomize is still an alpha feature and may be slated to be deprecated in a future version (see KEP 2953).

Plugin installation

Install using curl (on OSX or Linux):

OS=$(uname | tr '[:upper:]' '[:lower:]')
ARCH=$(uname -m | sed 's/x86_64/amd64/; s/aarch64/arm64/')
mkdir -p $HOME/.config/kustomize/plugin/khelm.mgoltzsche.github.com/v2/chartrenderer
curl -fsSL https://github.com/mgoltzsche/khelm/releases/latest/download/khelm-${OS}-${ARCH} > $HOME/.config/kustomize/plugin/khelm.mgoltzsche.github.com/v2/chartrenderer/ChartRenderer
chmod +x $HOME/.config/kustomize/plugin/khelm.mgoltzsche.github.com/v2/chartrenderer/ChartRenderer

or using go:

go get github.com/mgoltzsche/khelm/v2/cmd/khelm
mkdir -p $HOME/.config/kustomize/plugin/khelm.mgoltzsche.github.com/v2/chartrenderer
mv $GOPATH/bin/khelm $HOME/.config/kustomize/plugin/khelm.mgoltzsche.github.com/v2/chartrenderer/ChartRenderer

Plugin usage example

A plugin descriptor specifies the helm repository, chart, version and values that should be used in a kubernetes-style resource can be referenced in the generators section of a kustomization.yaml and can look as follows:

apiVersion: khelm.mgoltzsche.github.com/v2
kind: ChartRenderer
metadata:
  name: cert-manager # fallback for `name`
  namespace: cert-manager # fallback for `namespace`
repository: https://charts.jetstack.io
chart: cert-manager
version: 0.9.x
values:
  webhook:
    enabled: false

For all available fields see the table below.

More complete examples can be found within the example directory. For instance cert-manager can be rendered like this:

kustomize build --enable-alpha-plugins github.com/mgoltzsche/khelm/example/cert-manager

When using kustomize 3 the option is called --enable_alpha_plugins.

kustomize Containerized KRM Function

Similar to the kpt function approach, khelm can be used as Containerized KRM Function kustomize plugin. Though plugin support in kustomize is still an alpha feature, this form of extension seems destined to be graduated out of alpha (see KEP 2953).

This approach only works with kustomize>=v4.1.0.

Unlike the exec plugin strategy, this method does not require installation.

kustomize containerized KRM function usage example

A plugin descriptor specifies the helm repository, chart, version and values that should be used in a kubernetes-style resource can be referenced in the generators section of a kustomization.yaml and can look as follows:

apiVersion: khelm.mgoltzsche.github.com/v2
kind: ChartRenderer
metadata:
  name: cert-manager
  namespace: cert-manager
  annotations:
    config.kubernetes.io/function: |
      container:
        image: mgoltzsche/khelm:latest
        network: true
repository: https://charts.jetstack.io
chart: cert-manager
name: my-cert-manager-release
namespace: cert-manager
version: 0.9.x
values:
  webhook:
    enabled: false

For all available fields see the table below.

More complete examples can be found within the example/kustomize-krm directory.

For instance cert-manager can be rendered like this:

kustom