mirror of https://github.com/helm/helm
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
174 lines
6.7 KiB
174 lines
6.7 KiB
# 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.
|
|
|
|
## An Overview
|
|
|
|
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 help` and other places.
|
|
|
|
Helm plugins live in `$(helm home)/plugins`.
|
|
|
|
The Helm plugin model is partially modeled on Git's plugin model. To that end,
|
|
you may sometimes hear `helm` referred to as the _porcelain_ layer, with
|
|
plugins being the _plumbing_. This is a shorthand way of suggesting that
|
|
Helm provides the user experience and top level processing logic, while the
|
|
plugins do the "detail work" of performing a desired action.
|
|
|
|
## Installing a Plugin
|
|
|
|
A Helm plugin management system is in the works. But in the short term, plugins
|
|
are installed by copying the plugin directory into `$(helm home)/plugins`.
|
|
|
|
```console
|
|
$ cp -a myplugin/ $(helm home)/plugins/
|
|
```
|
|
|
|
If you have a plugin tar distribution, simply untar the plugin into the
|
|
`$(helm home)/plugins` directory.
|
|
|
|
## Building Plugins
|
|
|
|
In many ways, a plugin is similar to a chart. Each plugin has a top-level
|
|
directory, and then a `plugin.yaml` file.
|
|
|
|
```
|
|
$(helm home)/plugins/
|
|
|- keybase/
|
|
|
|
|
|- plugin.yaml
|
|
|- keybase.sh
|
|
|
|
```
|
|
|
|
In the example above, the `keybase` plugin is contained inside of a directory
|
|
named `keybase`. It has two files: `plugin.yaml` (required) and an executable
|
|
script, `keybase.sh` (optional).
|
|
|
|
The core of a plugin is a simple YAML file named `plugin.yaml`.
|
|
Here is a plugin YAML for a plugin that adds support for Keybase operations:
|
|
|
|
```
|
|
name: "keybase"
|
|
version: "0.1.0"
|
|
usage: "Integreate Keybase.io tools with Helm"
|
|
description: |-
|
|
This plugin provides Keybase services to Helm.
|
|
ignoreFlags: false
|
|
useTunnel: false
|
|
command: "$HELM_PLUGIN_DIR/keybase.sh"
|
|
```
|
|
|
|
The `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
|
|
plugin with `name: keybase` should be contained in a directory named `keybase`.
|
|
|
|
Restrictions on `name`:
|
|
|
|
- `name` cannot duplicate one of the existing `helm` top-level commands.
|
|
- `name` must be restricted to the characters ASCII a-z, A-Z, 0-9, `_` and `-`.
|
|
|
|
`version` is the SemVer 2 version of the plugin.
|
|
`usage` and `description` are both used to generate the help text of a command.
|
|
|
|
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.
|
|
|
|
The `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 `$TILLER_HOST` to the right local address for that
|
|
tunnel. But don't worry: if Helm detects that a tunnel is not necessary because
|
|
Tiller is running locally, it will not create the tunnel.
|
|
|
|
Finally, and most importantly, `command` is the command that this plugin will
|
|
execute when it is called. Environment variables are interpolated before the plugin
|
|
is executed. The pattern above illustrates the preferred way to indicate where
|
|
the plugin program lives.
|
|
|
|
There are some strategies for working with plugin commands:
|
|
|
|
- If a plugin includes an executable, the executable for a `command:` should be
|
|
packaged in the plugin directory.
|
|
- The `command:` line will have any environment variables expanded before
|
|
execution. `$HELM_PLUGIN_DIR` will 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 `-h` and `--help`.
|
|
Helm will use `usage` and `description` for `helm help` and `helm help myplugin`,
|
|
but will not handle `helm myplugin --help`.
|
|
|
|
## Environment Variables
|
|
|
|
When Helm executes a plugin, it passes the outer environment to the plugin, and
|
|
also injects some additional environment variables.
|
|
|
|
Variables like `KUBECONFIG` are set for the plugin if they are set in the
|
|
outer environment.
|
|
|
|
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`. So
|
|
`helm myplug` will have the short name `myplug`.
|
|
- `HELM_PLUGIN_DIR`: The directory that contains the plugin.
|
|
- `HELM_BIN`: The path to the `helm` command (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 `HELM_PATH`.
|
|
- `TILLER_HOST`: The `domain:port` to Tiller. If a tunnel is created, this
|
|
will point to the local endpoint for the tunnel. Otherwise, it will point
|
|
to `$HELM_HOST`, `--host`, or the default host (according to Helm's rules of
|
|
precedence).
|
|
|
|
While `HELM_HOST` _may_ be set, there is no guarantee that it will point to the
|
|
correct Tiller instance. This is done to allow plugin developer to access
|
|
`HELM_HOST` in its raw state when the plugin itself needs to manually configure
|
|
a connection.
|
|
|
|
## A Note on `useTunnel`
|
|
|
|
If a plugin specifies `useTunnel: true`, Helm will do the following (in order):
|
|
|
|
1. Parse global flags and the environment
|
|
2. Create the tunnel
|
|
3. Set `TILLER_HOST`
|
|
4. Execute the plugin
|
|
5. Close the tunnel
|
|
|
|
The tunnel is removed as soon as the `command` returns. So, for example, a
|
|
command cannot background a process and assume that that process will be able
|
|
to use the tunnel.
|
|
|
|
## A Note on Flag Parsing
|
|
|
|
When executing a plugin, Helm will parse global flags for its own use. Some of
|
|
these flags are _not_ passed on to the plugin.
|
|
|
|
- `--debug`: If this is specified, `$HELM_DEBUG` is set to `1`
|
|
- `--home`: This is converted to `$HELM_HOME`
|
|
- `--host`: This is converted to `$HELM_HOST`
|
|
- `--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 `-h` and `--help`. In all
|
|
other cases, plugins may use flags as appropriate.
|
|
|