The Helm Plugins Guide
A Helm 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
$HELM_PLUGINS. You can find the current value of this,
including the default value when not set in the environment, using the
helm env command.
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 plugin install https://github.com/adamreese/helm-env
If you have a plugin tar distribution, simply untar the plugin into the
$HELM_PLUGINS directory. You can also install tarball plugins
directly from url by issuing
helm plugin install https://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
$HELM_PLUGINS/ |- last/ | |- plugin.yaml |- last.sh
In the example above, the
last plugin is contained inside of a directory
last. It has two files:
plugin.yaml (required) and an executable
The core of a plugin is a simple YAML file named
plugin.yaml. Here is a plugin
YAML for a plugin that helps get the last release name:
name: "last" version: "0.1.0" usage: "get the last release name" description: "get the last release name" ignoreFlags: false command: "$HELM_BIN --host $TILLER_HOST list --short --max 1 --date -r" platformCommand: - os: linux arch: i386 command: "$HELM_BIN list --short --max 1 --date -r" - os: linux arch: amd64 command: "$HELM_BIN list --short --max 1 --date -r" - os: windows arch: amd64 command: "$HELM_BIN list --short --max 1 --date -r"
name is the name of the plugin. When Helm executes this 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: last 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.
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
--foo is silently discarded.
Finally, and most importantly,
command is the command
that this plugin will execute when it is called. The
defines the OS/Architecture specific variations of a command. The following
rules will apply in deciding which command to use:
platformCommandis present, it will be searched first.
- If both
archmatch the current platform, search will stop and the command will be used.
osmatches and there is no more specific
archmatch, the command will be used.
- If no
platformCommandmatch is found, the default
commandwill be used.
- If no matches are found in
commandis present, Helm will exit with an error.
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 pull 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
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 available Charts.
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
$HELM_CONFIG_HOME/repositories.yaml). A Downloader 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 for example
bin/mydownloader subcommand -d in the
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 outer
The following variables are guaranteed to be set:
HELM_PLUGINS: 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_DEBUG: Indicates if the debug flag was set by helm.
HELM_REGISTRY_CONFIG: The location for the registry configuration (if using). Note that the use of Helm with registries is an experimental feature.
HELM_REPOSITORY_CACHE: The path to the repository cache files.
HELM_REPOSITORY_CONFIG: The path to the repository configuration file.
HELM_NAMESPACE: The namespace given to the
helmcommand (generally using the
HELM_KUBECONTEXT: The name of the Kubernetes config context given to the
Additionally, if a Kubernetes configuration file was explicitly specified, it
will be set as the
A Note on Flag Parsing
When executing a plugin, Helm will parse global flags for its own use. None of these flags are passed on to the plugin.
--debug: If this is specified,
$HELM_DEBUGis set to
--registry-config: This is converted to
--repository-cache: This is converted to
--repository-config: This is converted to
-n: This is converted to
--kube-context: This is converted to
--kubeconfig: This is converted to
Plugins should display help text and then exit for
--help. In all
other cases, plugins may use flags as appropriate.
Providing shell auto-completion
As of Helm 3.2, a plugin can optionally provide support for shell auto-completion as part of Helm's existing auto-completion mechanism.
If a plugin provides its own flags and/or sub-commands, it can inform Helm of
them by having a
completion.yaml file located in the plugin's root directory.
completion.yaml file has the form:
name: <pluginName> flags: - <flag 1> - <flag 2> validArgs: - <arg value 1> - <arg value 2> commands: name: <commandName> flags: - <flag 1> - <flag 2> validArgs: - <arg value 1> - <arg value 2> commands: <and so on, recursively>
- All sections are optional but should be provided if applicable.
- Flags should not include the
- Both short and long flags can and should be specified. A short flag need not be associated with its corresponding long form, but both forms should be listed.
- Flags need not be ordered in any way, but need to be listed at the correct point in the sub-command hierarchy of the file.
- Helm's existing global flags are already handled by Helm's auto-completion
mechanism, therefore plugins need not specify the following flags
--kubeconfig, or any other global flag.
validArgslist provides a static list of possible completions for the first parameter following a sub-command. It is not always possible to provide such a list in advance (see the Dynamic Completion section below), in which case the
validArgssection can be omitted.
completion.yaml file is entirely optional. If it is not provided, Helm
will simply not provide shell auto-completion for the plugin (unless
Completion is supported by the plugin). Also, adding a
completion.yaml file is backwards-compatible and will not impact the behavior
of the plugin when using older helm versions.
As an example, for the
fullstatus plugin which has no
sub-commands but accepts the same flags as the
helm status command, the
completion.yaml file is:
name: fullstatus flags: - o - output - revision
A more intricate example for the
2to3 plugin, has a
completion.yaml file of:
name: 2to3 commands: - name: cleanup flags: - config-cleanup - dry-run - l - label - release-cleanup - s - release-storage - tiller-cleanup - t - tiller-ns - tiller-out-cluster - name: convert flags: - delete-v2-releases - dry-run - l - label - s - release-storage - release-versions-max - t - tiller-ns - tiller-out-cluster - name: move commands: - name: config flags: - dry-run
Also starting with Helm 3.2, plugins can provide their own dynamic shell auto-completion. Dynamic shell auto-completion is the completion of parameter values or flag values that cannot be defined in advance. For example, completion of the names of helm releases currently available on the cluster.
For the plugin to support dynamic auto-completion, it must provide an
executable file called
plugin.complete in its root directory. When the
Helm completion script requires dynamic completions for the plugin, it will
plugin.complete file, passing it the command-line that needs to be
plugin.complete executable will need to have the logic to
determine what the proper completion choices are and output them to standard
output to be consumed by the Helm completion script.
plugin.complete file is entirely optional. If it is not provided, Helm
will simply not provide dynamic auto-completion for the plugin. Also, adding a
plugin.complete file is backwards-compatible and will not impact the behavior
of the plugin when using older helm versions.
The output of the
plugin.complete script should be a new-line separated list
rel1 rel2 rel3
plugin.complete is called, the plugin environment is set just like when
the plugin's main script is called. Therefore, the variables
$HELM_KUBECONTEXT, and all other plugin variables will already be set, and
their corresponding global flags will be removed.
plugin.complete file can be in any executable form; it can be a shell
script, a Go program, or any other type of program that Helm can execute. The
plugin.complete file must have executable permissions for the user. The
plugin.complete file must exit with a success code (value 0).
In some cases, dynamic completion will require to obtain information from the
Kubernetes cluster. For example, the
helm fullstatus plugin requires a
release name as input. In the
fullstatus plugin, for its
script to provide completion for current release names, it can simply run
helm list -q and output the result.
If it is desired to use the same executable for plugin execution and for plugin
plugin.complete script can be made to call the main plugin
executable with some special parameter or flag; when the main plugin executable
detects the special parameter or flag, it will know to run the completion. In
plugin.complete could be implemented like this:
#!/usr/bin/env sh # "$@" is the entire command-line that requires completion. # It is important to double-quote the "$@" variable to preserve a possibly empty last parameter. $HELM_PLUGIN_DIR/status.sh --complete "$@"
fullstatus plugin's real script (
status.sh) must then look for the
--complete flag and if found, printout the proper completions.
Tips and tricks
- The shell will automatically filter out completion choices that don't match
user input. A plugin can therefore return all relevant completions without
removing the ones that don't match the user input. For example, if the
helm fullstatus ngin<TAB>, the
plugin.completescript can print all release names (of the
defaultnamespace), not just the ones starting with
ngin; the shell will only retain the ones starting with
- To simplify dynamic completion support, especially if you have a complex
plugin, you can have your
plugin.completescript call your main plugin script and request completion choices. See the Dynamic Completion section above for an example.
- To debug dynamic completion and the
plugin.completefile, one can run the following to see the completion results :
helm __complete <pluginName> <arguments to complete>. For example:
helm __complete fullstatus --output js<ENTER>,
helm __complete fullstatus -o json ""<ENTER>