Implementing Infrastructure as Code (IaC) with Terraform: Importing Existing Resources into Terraform Management

Welcome to our tutorial series, "Implementing Infrastructure as Code (IaC) with Terraform: A Comprehensive Tutorial". After diving into dependencies, we will focus on how Terraform can manage existing resources not originally created with Terraform. This blog post will guide you through importing existing resources into your Terraform project.

• Why Import Resources?

In some scenarios, you might already have infrastructure resources that weren't initially created with Terraform. Instead of recreating these resources, you can import them into Terraform. By doing so, you can manage these pre-existing resources using Terraform, alongside the rest of your Terraform created infrastructure.

• How to Import a Resource

Before importing a resource, you must write a resource block in your configuration. This block must specify the exact details of the existing resource, such as its type and name.

Here's an example of how to import an AWS instance with the ID i-abc1234d:

resource "aws_instance" "my_ec2" {
  # (resource arguments)
}        

Then, you can run the terraform import command, like so:

terraform import aws_instance.my_ec2 i-abc1234d        

This command tells Terraform to import the existing AWS instance with the ID i-abc1234d and manage it as the aws_instance.my_ec2 resource in your configuration.

• Understanding the Limitations

Although importing is a powerful feature, it's not without its limitations. Importing doesn't generate configuration. You must write it yourself to match the imported resources' settings. Additionally, not all resource types support importing.

• Keeping Your State Up-to-Date

After a successful import, the resource is included in the Terraform state and can be managed as usual with terraform apply, terraform plan, etc. Ensure your configuration matches reality to prevent Terraform from making unnecessary changes.

• Removing Imported Resources

If you no longer want Terraform to manage an imported resource, you can remove it from the Terraform state with terraform state rm, like so:

terraform state rm aws_instance.my_ec2        

Importing existing resources into Terraform's management is an essential aspect of infrastructure management. It allows you to seamlessly integrate resources regardless of how they were initially created.

In our next blog post, we'll explore using variables and outputs in Terraform, which enable re-usability and interactivity in your configurations. Stay tuned!