Custom Terraform Providers Development

What You’ll Learn 📚

• Understanding what Terraform providers are and why they matter
• Key terminology and concepts
• Step-by-step guide to creating a simple custom provider
• Progressively complex examples to build your skills
• Common questions and troubleshooting tips

Introduction to Terraform Providers

Before we jump into creating custom providers, let’s start with the basics. Terraform is an open-source tool that allows you to define and provision infrastructure using code. Providers are plugins that allow Terraform to interact with cloud providers, SaaS providers, and other APIs.

Think of providers as translators that help Terraform communicate with different services. Without them, Terraform wouldn’t know how to manage resources in AWS, Azure, or any other platform.

Key Terminology

• Provider: A plugin that enables Terraform to manage resources on a specific platform.
• Resource: The infrastructure component managed by Terraform, such as a virtual machine or a database.
• Schema: Defines the structure of a resource, including its properties and attributes.

Creating Your First Custom Provider

Let’s start with the simplest possible example: a custom provider that manages a fictional service called ‘MyService’.

package main

import (
    "github.com/hashicorp/terraform-plugin-sdk/helper/schema"
    "github.com/hashicorp/terraform-plugin-sdk/plugin"
)

func main() {
    plugin.Serve(&plugin.ServeOpts{
        ProviderFunc: func() *schema.Provider {
            return &schema.Provider{
                ResourcesMap: map[string]*schema.Resource{
                    "myservice_instance": resourceMyServiceInstance(),
                },
            }
        },
    })
}

func resourceMyServiceInstance() *schema.Resource {
    return &schema.Resource{
        Create: resourceMyServiceInstanceCreate,
        Read:   resourceMyServiceInstanceRead,
        Update: resourceMyServiceInstanceUpdate,
        Delete: resourceMyServiceInstanceDelete,
    }
}

func resourceMyServiceInstanceCreate(d *schema.ResourceData, m interface{}) error {
    // Logic to create a resource
    return nil
}

func resourceMyServiceInstanceRead(d *schema.ResourceData, m interface{}) error {
    // Logic to read a resource
    return nil
}

func resourceMyServiceInstanceUpdate(d *schema.ResourceData, m interface{}) error {
    // Logic to update a resource
    return nil
}

func resourceMyServiceInstanceDelete(d *schema.ResourceData, m interface{}) error {
    // Logic to delete a resource
    return nil
}

Expected Output

Progressively Complex Examples

Example 2: Adding Schema and Attributes

Let’s enhance our provider by defining a schema for ‘myservice_instance’.

func resourceMyServiceInstance() *schema.Resource {
    return &schema.Resource{
        Schema: map[string]*schema.Schema{
            "name": {
                Type:     schema.TypeString,
                Required: true,
            },
            "size": {
                Type:     schema.TypeString,
                Optional: true,
                Default:  "medium",
            },
        },
        Create: resourceMyServiceInstanceCreate,
        Read:   resourceMyServiceInstanceRead,
        Update: resourceMyServiceInstanceUpdate,
        Delete: resourceMyServiceInstanceDelete,
    }
}

Example 3: Implementing Create Logic

Now, let’s implement the create logic to make our provider actually do something.

func resourceMyServiceInstanceCreate(d *schema.ResourceData, m interface{}) error {
    name := d.Get("name").(string)
    size := d.Get("size").(string)
    // Logic to create the instance in MyService
    d.SetId(name) // Set the ID to the name for simplicity
    return nil
}

Example 4: Handling Read, Update, and Delete

Finally, let’s add logic for reading, updating, and deleting resources.

func resourceMyServiceInstanceRead(d *schema.ResourceData, m interface{}) error {
    // Logic to read the instance from MyService
    return nil
}

func resourceMyServiceInstanceUpdate(d *schema.ResourceData, m interface{}) error {
    // Logic to update the instance in MyService
    return nil
}

func resourceMyServiceInstanceDelete(d *schema.ResourceData, m interface{}) error {
    // Logic to delete the instance from MyService
    return nil
}

Common Questions and Answers

1. What is a Terraform provider?

   A Terraform provider is a plugin that enables Terraform to manage resources on a specific platform, such as AWS or Azure.

2. Why create a custom provider?

   Creating a custom provider allows you to manage resources on platforms not supported by existing providers or to extend the functionality of existing providers.

3. What language are Terraform providers written in?

   Terraform providers are typically written in Go, a statically typed, compiled programming language.

4. How do I test my custom provider?

   You can test your provider by writing Terraform configurations that use your provider and running them with the Terraform CLI.

5. What if my provider isn’t working?

   Check for errors in your code, ensure your API credentials are correct, and use logging to debug issues.

Troubleshooting Common Issues

If your provider isn’t working as expected, double-check your schema definitions and ensure your API calls are correct. Use logging to trace the flow of your code and identify where things might be going wrong.

Practice Exercises

• Create a custom provider for a simple API you have access to.
• Add additional resources to your provider and implement their logic.
• Experiment with different schema attributes and types.

For more information, check out the official Terraform documentation on writing custom providers.