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:

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

CLI

khelm also supports a helm-like template CLI.

Binary installation

OS=$(uname | tr '[:upper:]' '[:lower:]')
ARCH=$(uname -m | sed 's/x86_64/amd64/; s/aarch64/arm64/')
curl -fsSL https://github.com/mgoltzsche/khelm/releases/latest/download/khelm-${OS}-${ARCH} > khelm
chmod +x khelm
sudo mv khelm /usr/local/bin/khelm

Binary usage example

khelm template cert-manager --version=0.9.x --repo=https://charts.jetstack.io

For all available options see the table below.

Docker usage example

docker run mgoltzsche/khelm:latest template cert-manager --version=0.9.x --repo=https://charts.jetstack.io

Go API

The khelm Go API github.com/mgoltzsche/khelm/v2/pkg/helm provides a simple templating interface on top of the Helm Go API. It exposes a Helm struct that provides a Render() function that returns the rendered resources as kyaml objects.

Configuration options

Field	CLI	Description
chart	ARGUMENT	Chart file (if repository not set) or name.
version	--version	Chart version. Latest version is used if not specified.
repository	--repo	URL to the repository the chart should be loaded from.
valueFiles	-f	Locations of values files.
values	--set	Set values object or in CLI key1=val1,key2=val2.
apiVersions	--api-versions	Kubernetes api versions used for Capabilities.APIVersions.
kubeVersion	--kube-version	Kubernetes version used for Capabilities.KubeVersion.
name	--name	Release name used to render the chart.
verify	--verify	If enabled verifies the signature of all charts using the keyring (see Helm 3 provenance and integrity).
keyring	--keyring	GnuPG keyring file (default ~/.gnupg/pubring.gpg).
replaceLockFile	--replace-lock-file	Remove requirements.lock and reload charts when it is out of sync.
include		List of resource selectors that include matching resources from the output. If no selector specified all resources are included. Fails if a selector doesn't match any resource. Inclusions precede exclusions.
include[].apiVersion		Includes resources by apiVersion.
include[].kind		Includes resources by kind.
include[].namespace		Includes resources by namespace.
include[].name		Includes resources by name.
exclude		List of resource selectors that exclude matching resources from the output. Fails if a selector doesn't match any resource.
exclude[].apiVersion		Excludes resources by apiVersion.
exclude[].kind		Excludes resources by kind.
exclude[].namespace		Excludes resources by namespace.
exclude[].name		Excludes resources by name.
excludeCRDs	--skip-crds	If true Custom Resource Definitions are excluded from the output.
excludeHooks	--no-hooks	If enabled excludes chart hooks from the output.
namespace	--namespace	Set the namespace used by Helm templates.
namespacedOnly	--namespaced-only	If enabled fail on known cluster-scoped resources and those of unknown kinds.
forceNamespace	--force-namespace	Set namespace on all namespaced resources (and those of unknown kinds).
outputPath	--output	Path to write the output to. If it ends with / a kustomization is generated. (Not supported by the kustomize plugin.)
outputPathMapping[].outputPath		output path to which all resources should be written that match resourceSelectors. (Only supported by the kpt function.)
outputPathMapping[].selectors[].apiVersion		Selects resources by apiVersion.
outputPathMapping[].selectors[].kind		Selects resources by kind.
outputPathMapping[].selectors[].namespace		Selects resources by namespace.
outputPathMapping[].selectors[].name		Selects resources by name.
	--output-replace	If enabled replace the output directory or file (CLI-only).
	--trust-any-repo	If enabled repositories that are not registered within repositories.yaml can be used as well (env var KHELM_TRUST_ANY_REPO). Within the kpt function this behaviour can be disabled by mounting /helm/repository/repositories.yaml or disabling network access.
debug	--debug	Enables debug log and provides a stack trace on error.

Repository configuration

Repository credentials can be configured using Helm's repositories.yaml which can be passed through as Secret to generic build jobs. khelm downloads the corresponding repo index files when needed.

When running khelm as kpt function or within a container the repositories.yaml should be mounted to /helm/repository/repositories.yaml.

Unlike Helm khelm allows usage of any repository when repositories.yaml is not present or --trust-any-repo (env var KHELM_TRUST_ANY_REPO) is enabled.

Loading a chart from an OCI registry

Using Helm, you can store a Helm chart as OCI image within a container registry. To load a chart from an OCI registry using khelm, you can specify the OCI registry within the repository field, prefixed with oci://. The complete OCI image name is constructed from the repository and the chart field values, separated by /. For an example, see here and here.

When using a chart from an OCI registry, Helm's repository.yaml configuration is not used. Instead, Docker's config.json is used to read private registry credentials from, if any.

Helm support

• Helm 2 is supported by the v1 module version.
• Helm 3 is supported by the v2 module version.

Build and test

Build and test the khelm binary (requires Go 1.13) as well as the container image:

make clean khelm test check image e2e-test

The binary is written to build/bin/khelm.

Install the binary on your host at /usr/local/bin/khelm:

sudo make install