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Kubernetes Community Days Chennai profile image Suresh Kumar
Suresh Kumar for Kubernetes Community Days Chennai

Posted on • Originally published at sureshdsk.dev

How to create your first Helm plugin?

#kubernetes #devops #cloudnative #docker

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
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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>
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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
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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
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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
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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"
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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
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Test the plugin 

helm fullenv
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