The Helm Plugins Guide
Helm 2.1.0 introduced the concept of a client-side Helm plugin. A plugin is a
tool that can be accessed through the
helm CLI, but which is not part of the
built-in Helm codebase.
This guide explains how to use and create plugins.
Helm plugins are add-on tools that integrate seamlessly with Helm. They provide a way to extend the core feature set of Helm, but without requiring every new feature to be written in Go and added to the core tool.
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 helpand other places.
Helm plugins live in
The Helm plugin model is partially modeled on Git’s plugin model. To that end,
you may sometimes hear
helm referred to as the porcelain layer, with
plugins being the plumbing. This is a shorthand way of suggesting that
Helm provides the user experience and top level processing logic, while the
plugins do the “detail work” of performing a desired action.
Installing a Plugin
Plugins are installed using the
$ helm plugin install <path|url> command. You can pass in a path to a plugin on your local file system or a url of a remote VCS repo. The
helm plugin install command clones or copies the plugin at the path/url given into
$ (helm home)/plugins
$ helm plugin install https://github.com/technosophos/helm-template
If you have a plugin tar distribution, simply untar the plugin into the
$(helm home)/plugins directory.
You can also install tarball plugins directly from url by issuing
helm plugin install http://domain/path/to/plugin.tar.gz
In many ways, a plugin is similar to a chart. Each plugin has a top-level
directory, and then a
$(helm home)/plugins/ |- keybase/ | |- plugin.yaml |- keybase.sh
In the example above, the
keybase plugin is contained inside of a directory
keybase. It has two files:
plugin.yaml (required) and an executable
The core of a plugin is a simple YAML file named
Here is a plugin YAML for a plugin that adds support for Keybase operations:
name: "keybase" version: "0.1.0" usage: "Integrate Keybase.io tools with Helm" description: |- This plugin provides Keybase services to Helm. ignoreFlags: false useTunnel: false command: "$HELM_PLUGIN_DIR/keybase.sh"
name is the name of the plugin. When Helm executes it plugin, this is the
name it will use (e.g.
helm NAME will invoke this plugin).
name should match the directory name. In our example above, that means the
name: keybase should be contained in a directory named
namecannot duplicate one of the existing
namemust be restricted to the characters ASCII a-z, A-Z, 0-9,
version is the SemVer 2 version of the plugin.
description are both used to generate the help text of a command.
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
is silently discarded.
useTunnel switch indicates that the plugin needs a tunnel to Tiller. This
should be set to
true anytime a plugin talks to Tiller. It will cause Helm
to open a tunnel, and then set
$TILLER_HOST to the right local address for that
tunnel. But don’t worry: if Helm detects that a tunnel is not necessary because
Tiller is running locally, it will not create the tunnel.
Finally, and most importantly,
command is the command that this plugin will
execute when it is called. Environment variables are interpolated before the plugin
is executed. The pattern above illustrates the preferred way to indicate where
the plugin program lives.
There are some strategies for working with plugin commands:
- If a plugin includes an executable, the executable for a
command:should be packaged in the plugin directory.
command:line will have any environment variables expanded before execution.
$HELM_PLUGIN_DIRwill point to the plugin directory.
- The command itself is not executed in a shell. So you can’t oneline a shell script.
- Helm injects lots of configuration into environment variables. Take a look at the environment to see what information is available.
- Helm makes no assumptions about the language of the plugin. You can write it in whatever you prefer.
- Commands are responsible for implementing specific help text for
--help. Helm will use
helm help myplugin, but will not handle
helm myplugin --help.
By default, Helm is able to fetch Charts using HTTP/S. As of Helm 2.4.0, plugins can have a special capability to download Charts from arbitrary sources.
Plugins shall declare this special capability in the
plugin.yaml file (top level):
downloaders: - command: "bin/mydownloader" protocols: - "myprotocol" - "myprotocols"
If such plugin is installed, Helm can interact with the repository using the specified
protocol scheme by invoking the
command. The special repository shall be added
similarly to the regular ones:
helm repo add favorite myprotocol://example.com/
The rules for the special repos are the same to the regular ones: Helm must be able
to download the
index.yaml file in order to discover and cache the list of
The defined command will be invoked with the following scheme:
command certFile keyFile caFile full-URL. The SSL credentials are coming from the
repo definition, stored in
plugin is expected to dump the raw content to stdout and report errors on stderr.
The downloader command also supports sub-commands or arguments, allowing you to specify
bin/mydownloader subcommand -d in the
plugin.yaml. This is useful
if you want to use the same executable for the main plugin command and the downloader
command, but with a different sub-command for each.
When Helm executes a plugin, it passes the outer environment to the plugin, and also injects some additional environment variables.
KUBECONFIG are set for the plugin if they are set in the
The following variables are guaranteed to be set:
HELM_PLUGIN: The path to the plugins directory
HELM_PLUGIN_NAME: The name of the plugin, as invoked by
helm myplugwill have the short name
HELM_PLUGIN_DIR: The directory that contains the plugin.
HELM_BIN: The path to the
helmcommand (as executed by the user).
HELM_HOME: The path to the Helm home.
HELM_PATH_*: Paths to important Helm files and directories are stored in environment variables prefixed by
domain:portto Tiller. If a tunnel is created, this will point to the local endpoint for the tunnel. Otherwise, it will point to
--host, or the default host (according to Helm’s rules of precedence).
HELM_HOST may be set, there is no guarantee that it will point to the
correct Tiller instance. This is done to allow plugin developer to access
HELM_HOST in its raw state when the plugin itself needs to manually configure
A Note on
If a plugin specifies
useTunnel: true, Helm will do the following (in order):
- Parse global flags and the environment
- Create the tunnel
- Execute the plugin
- Close the tunnel
The tunnel is removed as soon as the
command returns. So, for example, a
command cannot background a process and assume that process will be able
to use the tunnel.
A Note on Flag Parsing
When executing a plugin, Helm will parse global flags for its own use. Some of these flags are not passed on to the plugin.
--debug: If this is specified,
$HELM_DEBUGis set to
--home: This is converted to
--host: This is converted to
--kube-context: This is simply dropped. If your plugin uses
useTunnel, this is used to set up the tunnel for you.
Plugins should display help text and then exit for
--help. In all
other cases, plugins may use flags as appropriate.