Terraform Notes

My notes on Terraform

What is Terraform

Terraform is an open-source infrastructure as code software tool that enables users to define and provision infrastructure resources through code. It allows users to write, plan, and create infrastructure resources in a safe and efficient manner.

With Terraform, users can manage infrastructure for a variety of cloud providers, such as AWS, Azure, and Google Cloud.

One of the key benefits of using Terraform is that it provides a common language for users to describe their infrastructure resources, making it easier to understand and collaborate on projects. It also has a wide range of built-in integrations with different infrastructure providers, which makes it easy to get started with Terraform and start managing resources quickly.

In addition, Terraform has a number of features that make it a powerful tool for managing infrastructure resources, including:

• Version control: Terraform enables users to version control their infrastructure and roll back changes if necessary. This makes it easier to manage and track changes to infrastructure resources.

• Resource graph: Terraform generates a visual representation of the resources it manages, which makes it easier to understand the relationships between resources and how they depend on each other.

• Resource provisioning: Terraform can create, update, and delete resources in a safe and predictable manner, ensuring that resources are created in the correct order and that dependencies are taken into account.

Overall, Terraform is a powerful and flexible tool for managing infrastructure resources that is well-suited for a wide range of use cases. Whether you are managing a small infrastructure for a personal project or a large, complex infrastructure for a business, Terraform can help you manage your resources in a safe, efficient, and predictable manner

Installing Terraform

The easiest way to install Terraform on a Mac is through Homebrew. If you don’t have Homebrew installed, you can install it by running the following command in your terminal:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

Once Homebrew is installed, you can install Terraform by running the following command:

brew install terraform

This will install the latest version of Terraform. To confirm that Terraform was installed successfully, run the following command:

terraform -v

You should see the version number of Terraform displayed in your terminal.

Terraform functions and statements

replace: replace string

resource "aws_s3_bucket" "photo_storage" {
  bucket = replace("${var.component}-${var.env}-photo-storage", "_", "-")

  tags = {
    Name        = "Photo Storage"
    Environment = var.env
  }
}

for_each: used with resources and data sources to create multiple instances based on a set or a map. It allows you to iterate over a collection and create a separate instance of the resource or data source for each item in the collection.

In the example:

data "google_compute_subnetwork" "all_subnets" {
  for_each = toset(data.google_compute_network.ids_network.subnetworks_self_links)

  self_link = each.value
  project   = var.project_id
}

for_each is used with the google_compute_subnetwork data source to fetch information about all subnetworks in the given network. The toset() function is used to convert the list of subnetwork self-links to a set. The each.value reference represents the current item in the iteration.

dynamic: used within resource blocks to dynamically generate nested blocks based on a given set of data. It allows you to create a nested block for each item in a collection without having to write out each block manually.

In the example:

resource "google_compute_packet_mirroring" "ids_packet_mirroring" {
  ...
  mirrored_resources {
    dynamic "subnetworks" {
      for_each = data.google_compute_subnetwork.all_subnets
      content {
        url = subnetworks.value.id
      }
    }
  }
}

dynamic is used within the mirrored_resources block of the google_compute_packet_mirroring resource to create a subnetworks block for each subnetwork in the data.google_compute_subnetwork.all_subnets data source. The for_each statement iterates over the subnetworks, and the content block defines the structure of the generated subnetworks block. The subnetworks.value reference represents the current item in the iteration, in this case, a subnetwork object.

AWS Lambda Integration

The integration method is always POST even though your incoming request http method is GET

resource "aws_api_gateway_method" "get_job" {
  rest_api_id      = aws_api_gateway_rest_api.service_agent.id
  resource_id      = aws_api_gateway_resource.jobs.id
  http_method      = "GET"
  authorization    = "NONE"
  api_key_required = true
}

resource "aws_api_gateway_integration" "get_job" {
  rest_api_id = aws_api_gateway_rest_api.service_agent.id
  resource_id = aws_api_gateway_resource.jobs.id
  http_method = aws_api_gateway_method.get_job.http_method

  integration_http_method = "POST"
  type                    = "AWS_PROXY"
  uri                     = aws_lambda_function.get_job.invoke_arn
}

resource "aws_lambda_permission" "get_job" {
  statement_id  = "AllowExecutionFromAPIGateway"
  action        = "lambda:InvokeFunction"
  function_name = aws_lambda_function.get_job.arn
  principal     = "apigateway.amazonaws.com"
  source_arn    = "${aws_api_gateway_rest_api.service_agent.execution_arn}/*/*/*"
}

TF_VAR_

Environment variables can be used to set terraform variables. The environment variable must be in the format of TF_VAR_name

export TF_VAR_region=eu-west-1
export TF_VAR_ami=ami-049d8641
export TF_VAR_list='[1,2,3]'
export TF_VAR_map='{ foo = "bar", baz = "qux" }'

Examples

AWS Lambda

data "archive_file" "update_job" {
  type        = "zip"
  source_dir  = "../dist/update-job"
  output_path = "../dist/update-job.zip"
}

resource "aws_lambda_function" "update_job" {
  function_name = "${var.component}_${var.env}_update_job"
  filename      = data.archive_file.update_job.output_path

  runtime     = "nodejs18.x"
  memory_size = var.memory_size
  timeout     = var.timeout
  handler     = "index.handler"

  source_code_hash = data.archive_file.update_job.output_base64sha256
  role             = aws_iam_role.iam_lambda_role.arn

  environment {
    variables = {
      run_env = var.env
    }
  }
}