Developing Custom Terraform Plugins

Terraform empowers you to automate infrastructure provisioning across various cloud platforms, streamlining your workflow. But what if your needs extend beyond these built-in functionalities, and your infrastructure relies on a unique API? Here’s where custom Terraform providers come to the rescue!

Imagine managing any service with an API directly through Terraform. Custom providers unlock this potential, granting you complete control and seamless integration within your existing workflows. In this blog, we’ll explore why you might need a custom provider and then guide you through the creation process step-by-step.

What is a Terraform provider?

A Terraform provider is a Go binary plugin responsible for interacting with cloud APIs or self-hosted APIs. The provider implements a set of resources and data sources that Terraform can manage. In a nutshell, Providers bridge the gap between Terraform and external services by translating Terraform’s configuration language (HCL) into API calls, and the target service understands and interprets the responses back to Terraform. There are built-in providers for many services, but custom providers unlock the potential to manage resources from any unique API.

Terraform can be broken down into two key components: Terraform Core and Terraform Plugins

• Terraform Core: This is the Terraform binary written in the GO programming language that communicates with plugins through RPC (remote procedure calls). Terraform core is responsible for reading the configuration, building the resource dependency graph, managing the resources’ states, executing Terraform plans (e.g., Terraform plan, apply, destroy, refresh), and communicating with the custom Terraform providers/plugins.
• Terraform Plugins: These are separately executable binaries written in Go that communicate with Terraform Core over an RPC interface. Each plugin exposes an implementation for a specific application. Plugin is responsible for communicating with the actual application/service eg. initialization of REST libraries used to make API calls, authentication for application.

Writing a Terraform plugin

Let’s write a simple custom Terraform plugin that will help configure the simple Python-based Flask application.

Prerequisites:

1. Let’s create a simple Flask web application that can manage the information for a single resource: a Person. This application exposes the API to perform the CRUD operations for the person. Please refer here to install person app.
2. Install Go 1.13+. Please refer here.
3. Install Terraform 0.13+. (read more..)