Create Terraform Scripts for an Existing Infrastructure

Introduction

This blog explains the solution approach and steps to create Terraform Scripts for an Existing Infrastructure. Here, AWS will be used for that infrastructure.

Solution Design

Implementation Steps

• As a first step, need to identify the list of resources that already exists in the AWS infrastructure. These resources might have created manually To identify the already created (could be manually using console) resources in AWS, the below-listed approach will help.

  • Approach 1: Using AWS Console Tag Editor search, can identify the list resources created by resource type.

  • Approach 2: Using AWS CLI command (Example : aws configservice list-discovered-resources --resource-type AWS::EC2::VPC ), can list down the resource list and its ids. Here, refer https://docs.aws.amazon.com/cli/latest/reference/configservice/list-discovered-resources.html#options

• Create terraform script. Example:

terraform {
  required_providers {
    aws = {
        source = "hashicorp/aws"
        version = ">= 0.15.0"
    }
  }
}

provider "aws" {
  profile = "default"
  region = "us-west-2"
}

• Run command terraform init to initialize the terraform and make sure the terraform connectivity with the infrastructure.

• Update terraform resource with resource name. Refer: Terraform documentation for the exact resource name and mandatory parameter configuration for import functionality.

resource "aws_vpc" "test_vpc" {
  cidr_block = "10.0.0.0/16"
}

Here, cidr_block is mandatory. So added this parameter alone

• Import the resource from existing infrastructure using the import command with the exact resource id noted in first step. Example terraform import aws_vpc.test_vpc vpc-0841e2b7a945624b6.

• Once imported, use the command terraform show to show the exact resource details to update back in terraform script.

• then, run terraform validate and cleanup all the error need to be fixed. Mostly the id attributes need to be removed which was copied from show command.

• Now, after all the errors fixed, can run command terranform plan which should result No changes. Infrastructure is up-to-date.. This confirms terraform scripts and AWS infrastructure matches no need changes. Moving, forward can start making changes in terraform script and push it to AWS environment.