terraform/website/source/docs/plugins/basics.html.md

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Plugin Basics

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.

Advanced topic! Plugin development is a highly advanced topic in Terraform, and is not required knowledge for day-to-day usage. If you don't plan on writing any plugins, we recommend not reading this section of the documentation.

How it Works

The plugin system for Terraform is based on multi-process RPC. Every provider, provisioner, etc. in Terraform is actually a separate compiled binary. You can see this when you download Terraform: the Terraform package contains multiple binaries.

Terraform executes these binaries in a certain way and uses Unix domain sockets or network sockets to perform RPC with the plugins.

If you try to execute a plugin directly, an error will be shown:

$ terraform-provider-aws
This binary is a Terraform plugin. These are not meant to be
executed directly. Please execute `terraform`, which will load
any plugins automatically.

The code within the binaries must adhere to certain interfaces. The network communication and RPC is handled automatically by higher-level Terraform libraries. The exact interface to implement is documented in its respective documentation section.

Installing a Plugin

To install a plugin, put the binary somewhere on your filesystem, then configure Terraform to be able to find it. The configuration where plugins are defined is ~/.terraformrc for Unix-like systems and %APPDATA%/terraform.rc for Windows.

An example that configures a new provider is shown below:

providers {
	privatecloud = "/path/to/privatecloud"
}

The key privatecloud is the prefix of the resources for that provider. For example, if there is privatecloud_instance resource, then the above configuration would work. The value is the name of the executable. This can be a full path. If it isn't a full path, the executable will be looked up on the PATH.

Developing a Plugin

Developing a plugin is simple. The only knowledge necessary to write a plugin is basic command-line skills and basic knowledge of the Go programming language.

Note: A common pitfall is not properly setting up a $GOPATH. This can lead to strange errors. You can read more about this here to familiarize yourself.

Create a new Go project somewhere in your $GOPATH. If you're a GitHub user, we recommend creating the project in the directory $GOPATH/src/github.com/USERNAME/terraform-NAME, where USERNAME is your GitHub username and NAME is the name of the plugin you're developing. This structure is what Go expects and simplifies things down the road.

With the directory made, create a main.go file. This project will be a binary so the package is "main":

package main

import (
	"github.com/hashicorp/terraform/plugin"
)

func main() {
	plugin.Serve(new(MyPlugin))
}

And that's basically it! You'll have to change the argument given to plugin.Serve to be your actual plugin, but that is the only change you'll have to make. The argument should be a structure implementing one of the plugin interfaces (depending on what sort of plugin you're creating).

While its not strictly necessary, Terraform plugins follow specific naming conventions. The format of the plugin binaries are terraform-TYPE-NAME. For example, terraform-provider-aws. We recommend you follow this convention to help make it clear what your plugin does to users.