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...and one other reference to the application data directory. Context: https://docs.microsoft.com/en-us/windows/desktop/shell/knownfolderid#folderid_roamingappdata In newer Windows versions, the folder accessible as `%APPDATA%` (and via various APIs) is actually at something like "documents and settings\user\application data\roaming", while earlier versions omit the "\roaming" part of the path. This means you can confuse people by referring to the "application data" directory by its human name, because "roaming" is the real application data directory, but it looks like a subdirectory of "application data". Thus, it's less confusing to just use the `%APPDATA%` variable, with the added benefit that you can copy and paste the path and it'll just work in most places.
102 lines
3.9 KiB
Markdown
102 lines
3.9 KiB
Markdown
---
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layout: "docs"
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page_title: "Plugin Basics"
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sidebar_current: "docs-plugins-basics"
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description: |-
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This page documents the basics of how the plugin system in Terraform works, and how to setup a basic development environment for plugin development if you're writing a Terraform plugin.
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---
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# Plugin Basics
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~> **Advanced topic!** Plugin development is a highly advanced
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topic in Terraform, and is not required knowledge for day-to-day usage.
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If you don't plan on writing any plugins, this section of the documentation is
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not necessary to read. For general use of Terraform, please see our
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[Intro to Terraform](/intro/index.html) and [Getting
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Started](/intro/getting-started/install.html) guides.
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This page documents the basics of how the plugin system in Terraform
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works, and how to setup a basic development environment for plugin development
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if you're writing a Terraform plugin.
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## How it Works
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Terraform providers and provisioners are provided via plugins. Each plugin
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exposes an implementation for a specific service, such as AWS, or provisioner,
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such as bash. Plugins are executed as a separate process and communicate with
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the main Terraform binary over an RPC interface.
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More details are available in
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_[Plugin Internals](/docs/internals/internal-plugins.html)_.
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The code within the binaries must adhere to certain interfaces.
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The network communication and RPC is handled automatically by higher-level
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Terraform libraries. The exact interface to implement is documented
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in its respective documentation section.
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## Installing Plugins
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The [provider plugins distributed by HashiCorp](/docs/providers/index.html) are
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automatically installed by `terraform init`. Third-party plugins (both
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providers and provisioners) can be manually installed into the user plugins
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directory, located at `%APPDATA%\terraform.d\plugins` on Windows and
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`~/.terraform.d/plugins` on other systems.
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For more information, see:
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- [Configuring Providers](/docs/configuration/providers.html)
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- [Configuring Providers: Third-party Plugins](/docs/configuration/providers.html#third-party-plugins)
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For developer-centric documentation, see:
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- [How Terraform Works: Plugin Discovery](/docs/extend/how-terraform-works.html#discovery)
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## Developing a Plugin
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Developing a plugin is simple. The only knowledge necessary to write
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a plugin is basic command-line skills and basic knowledge of the
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[Go programming language](http://golang.org).
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-> **Note:** A common pitfall is not properly setting up a
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<code>$GOPATH</code>. This can lead to strange errors. You can read more about
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this [here](https://golang.org/doc/code.html) to familiarize
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yourself.
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Create a new Go project somewhere in your `$GOPATH`. If you're a
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GitHub user, we recommend creating the project in the directory
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`$GOPATH/src/github.com/USERNAME/terraform-NAME`, where `USERNAME`
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is your GitHub username and `NAME` is the name of the plugin you're
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developing. This structure is what Go expects and simplifies things down
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the road.
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The `NAME` should either begin with `provider-` or `provisioner-`,
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depending on what kind of plugin it will be. The repository name will,
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by default, be the name of the binary produced by `go install` for
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your plugin package.
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With the package directory made, create a `main.go` file. This project will
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be a binary so the package is "main":
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```golang
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package main
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import (
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"github.com/hashicorp/terraform/plugin"
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)
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func main() {
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plugin.Serve(new(MyPlugin))
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}
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```
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The name `MyPlugin` is a placeholder for the struct type that represents
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your plugin's implementation. This must implement either
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`terraform.ResourceProvider` or `terraform.ResourceProvisioner`, depending
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on the plugin type.
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To test your plugin, the easiest method is to copy your `terraform` binary
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to `$GOPATH/bin` and ensure that this copy is the one being used for testing.
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`terraform init` will search for plugins within the same directory as the
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`terraform` binary, and `$GOPATH/bin` is the directory into which `go install`
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will place the plugin executable.
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