How to create your first Helm plugin?

Helm

Helm helps you manage Kubernetes applications using helm charts. Helm Charts help you define, install, and upgrade Kubernetes applications.

Example:

# add chart repository
helm repo add bitnami https://charts.bitnami.com/bitnami

# update charts
helm repo update

# install mysql using helm chart by bitnami
helm install bitnami/mysql --generate-name

Helm plugins

Helm plugins provide a way to extend Helm features without modifying the helm core codebase.

Helm plugins have the following features:

• They can be added and removed from a Helm installation without impacting the core Helm tool.
• They can be written in any programming language.
• They integrate with Helm, and will show up in helm help and other places.

Helm plugins are stored in $HELM_PLUGINS directory, you can change this using helm env command.

Install a helm plugin

A Helm plugin can be installed from a git repo, a tar release or from a local directory.

helm plugin install <path|url>

Helm plugin anatomy

A helm plugin constists of a plugin.yaml file, which has the plugin definition and its associated commands.

─ fullenv
   ├── plugin.yaml
   └── run.sh

plugin definition

plugin.yaml defines the name, usage, description and command to run when invoked.

• The Command can point to your own script of any programming language.
• The ignoreFlags switch tells Helm to not pass flags to the plugin.

So if a plugin is called with helm myplugin --foo and ignoreFlags: true, then --foo is silently discarded.

plugin.yaml

name: fullenv
usage: "show env vars"
description: "show all env vars"
command: "$HELM_PLUGIN_DIR/run.sh"
ignoreFlags: true

run.sh - just prints helm environment variables.

#!/bin/sh
echo $HELM_PLUGIN_NAME
echo $HELM_PLUGIN_DIR
echo $HELM_PLUGINS
echo $HELM_REPOSITORY_CONFIG
echo $HELM_REPOSITORY_CACHE
echo $HELM_BIN

Platform specific commands

Helm plugin commands can be configured to target a os platform and architecture.

name: fullenv
usage: "show env vars"
description: "show all env vars"
command: "$HELM_PLUGIN_DIR/run.sh"
platformCommand:
  - os: linux
    arch: i386
    command: "$HELM_PLUGIN_DIR/run.sh"
  - os: linux
    arch: amd64
    command: "$HELM_PLUGIN_DIR/run.sh"

Helm follows the below rules to choose a command.

• If platformCommand is present, it will be searched first.
• If both os and arch match the current platform, search will stop and the command will be used.
• If os matches and there is no more specific arch match, the command will be used.
• If no platformCommand match is found, the default command will be used.
• If no matches are found in platformCommand and no command is present, Helm will exit with an error.

Install the plugin

cd into the plugin directory and then run the command below

# install
helm plugin install .

# check if the installation is successful
helm plugin list

Test the plugin

helm fullenv

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