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Thomas Brittain
Thomas Brittain

Posted on • Updated on • Originally published at ladvien.com

How to Set Up Terraform and Terragrunt

#aws #terraform #terragrunt #iac

Last time, we set up our local machine for accessing AWS programmatically. This will allow us to use Terraform and Terragrunt to easily create all infrastructure needed for our data warehouse. Now, let's set up Terragrunt and Terraform.

Install Terraform

Navigate to the Terraform downloads page:

After installing Terraform enter the following in the terminal:

terraform --version
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You should be greeted with output similar to:

Terraform v1.2.8
on darwin_arm64
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Install Terragrunt

Terragrunt is a thin wrapper for Terraform, having a few additional tools for managing IaC projects.

Download and install it:

After installing Terragrunt type the following in the terminal:

terragrunt --version
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You should get the Terragrunt version as output:

terragrunt version v0.38.7
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Create a Git Repository

I'll be using Github, but any git hosting service should be similar.

Use My IaC Template

If you want to skip the next part and use my template repository:

Visit the page and fork the repository into your Github account, then, clone it locally.

Open a terminal and type, replacing <YOUR_GITHUB_NAME> with your Github username:

git clone https://github.com/<YOUR_GITHUB_NAME>/self_sensored_iac.git
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I'll explain in the next section why this repository is setup the way it is.

Create an IaC Template

In Github, create a new repository and call it self_sensored_iac or whatever name you'd like to give your personal enterprise. Then clone this repository locally.

create-repository-github

Set "Add README.md" and "Add .gitignore". For the .gitignore template, select Terraform.

setup-infrastructure-as-code-repository-in-github

git clone https://github.com/<YOUR_NAME>/<YOUR_REPO>.git
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Setup Enterprise Terragrunt Project

Whew, we made it. Our work machine is set up. Now, we need to create a Terragrunt project.

The idea of our Terragrunt project is to separate code into two major categories. First, common_modules will contain a folder for each of the major resources you plan to deploy. Imagine these are class definitions. The second category contains all the inputs needed to initialize the resources defined in the common_modules.

The easiest way to create this project is with a folder structure like this:

.
├── README.md
├── common_modules
│   ├── vpc
│   │   ├── data.tf
│   │   ├── main.tf
│   │   ├── outputs.tf
│   │   └── variables.tf
├── empty.yaml
└── prod
    ├── environment.yaml
    └── us-west-2
        ├── aws_provider.tf
        ├── terragrunt.hcl
        ├── region.yaml
        └── vpc
           └── terragrunt.hcl
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common_modules

As I mentioned, the commond_modules is similar to a class in object-oriented programming. It is a blueprint of a resource and should be coded in a way to provide appropriate flexibility. That is, if we create a blueprint to set up a VPC, it should probably take only a few inputs. These inputs will then change certain behavior per deployment of the resource.

In Terragrunt, a module is defined by a folder containing a collection of files ending in .tf. Collectively, these files tell Terraform how to create the needed infrastructure within AWS.

Let's look at the VPC code. It is in ./commond_modules/vpc/ As the files may suggest, main.tf is where most of the magic happens. Let's take a look:

module "vpc" {
  source = "terraform-aws-modules/vpc/aws"

  name = "${var.vpc_name}"
  cidr = "${var.vpc_network_prefix}.0.0/16"

  azs             = ["${var.region}a", "${var.region}b", "${var.region}c"]
  private_subnets = ["${var.vpc_network_prefix}.1.0/24", "${var.vpc_network_prefix}.2.0/24", "${var.vpc_network_prefix}.3.0/24"]
  public_subnets  = ["${var.vpc_network_prefix}.101.0/24", "${var.vpc_network_prefix}.102.0/24", "${var.vpc_network_prefix}.103.0/24"]

  enable_nat_gateway = false
  single_nat_gateway = true

  enable_dns_hostnames = true
  enable_dns_support = true

  tags = {
    Terraform = "true"
    Environment = "${var.environment_name}"
  }

  nat_gateway_tags = {
    Project = "${var.project_name}"
    Terraform = "true"
    Environment = "${var.environment_name}"
  }
}

resource "aws_security_group" "allow-ssh" {
  vpc_id      = data.aws_vpc.vpc_id.id
  name        = "allow-ssh"
  description = "Security group that allows ssh and all egress traffic"

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

  // Allow direct access to the EC2 boxes for me only.
  ingress {
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["${chomp(data.http.myip.body)}/32"]
  }

  tags = {
    Name = "allow-ssh"
  }

}
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Note, the module "vpc" is a prebuilt VPC module, so what we are doing is grabbing a VPC module provided by AWS:

Which handles a lot of the boilerplate setup. Then, we take care of even more settings we don't often want to change. That is, every place you see ${var.something} we are creating inputs that may be changed at the time of deployment.

Take the VPC name parameter for example:

module "vpc" {
  source = "terraform-aws-modules/vpc/aws"

  name = "${var.vpc_name}"
  ...
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Keep this in mind while we look at the prod folder:

prod

The production folder and subfolder are where we consume the modules we have defined in the common_modules folder. Let's look at the /prod/us-west-2/terragrunt.hcl file.

terraform {
  source = "../../..//common_modules/vpc"
}

...

inputs = {
    vpc_name = "ladviens-analytics-stack-vpc"
    vpc_network_prefix = "10.17"
}
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The important definitions here are the terraform and inputs maps. The terraform map will tell Terragrunt, when run from this folder, to treat the source directory specified as a Terraform module.

The inputs map contains all of the variables needed to make sure VPC is deployed correctly. You'll notice, we have hardcoded everything in our vpc module but the name and network prefix. This may not be ideal for you. Feel free to change anything in the vpc module files to make it more reusable. And to help, I'll provide an example a bit later in the article.

Planning Our VPC

One of the joys of Terraform is its ability to report what infrastructure would be built before it is actually built. This can be done by running the terragrunt plan command at the terminal when inside the directory ./prod/us-west-2/vpc/.

At the terminal, navigate to the VPC definition directory:

cd prod/us-west-2/vpc
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Then run:

terragrunt plan
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You should end up with something like this:

Initializing modules...
Downloading registry.terraform.io/terraform-aws-modules/vpc/aws 3.18.1 for vpc...
- vpc in .terraform/modules/vpc

Initializing the backend...
...
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After a little while, Terraform should print a complete plan. This consists of a bunch of diffs. The green + are indicating what will be added. Yellow ~ flagging what will be changed. And a red - indicates resources to be destroyed. At this point, the plan will return showing everything that needs to be built.

Deploying the VPC

Let's deploy the VPC. Still in the ./prod/us-west-2/vpc/ directory, type:

terragrunt apply
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Again Terraform will assess the inputs in your terragrunt.hcl and the module definitions in ./common_modules/vpc/ then print out what will be created. However, this time it will ask if you want to deploy. Type yes and hit return.

Terraform will begin requesting resources in AWS on your behalf. Once it is done, I encourage you to open your AWS console and navigate to the "VPC" section. You should see a newly created VPC alongside your default VPC (the one with no name).

vpc-created-terraform

Huzzah!

Modifying modules to increase reusability

Let's look at how to add a new input to the vpc module we've made. Open the ./common_modules/vpc/variables.tf file go to the bottom of the file and add:

variable "enable_dns" {

}
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We will add more to it, but this is good for now.

A variable in Terraform acts as an input for a module or file. With the enable_dns variable in place, in the terminal, in the directory ./prod/us-west-2/vpc/, run the following:

terragrunt apply
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This time you should be prompted with:

var.enable_dns
  Enter a value:
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This is Terragrunt seeing a variable definition and there's no matching input in your ./prod/us-west-2/vpc/terragrunt.hcl, so it prompts at the command line. This can come in handy, say, having a variable that is a password and you don't want it hard coded in your repository.

But let's go ahead and adjust our terragrunt.hcl to contain the needed input. In the file ./prod/us-west-2/vpc/terragrunt.hcl add the following enable_dns = true. The result should look like this:

terraform {
  source = "../../..//common_modules/vpc"
}

include {
  path = find_in_parent_folders()
}

inputs = {
    vpc_name = "ladviens-analytics-stack-vpc"
    vpc_network_prefix = "10.17"
    enable_dns = true
}
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Now run terragrunt apply again. This time Terragrunt should find the input in the terragrunt.hcl file matching the variable name in the module.

Of course, we're not quite done. We still need to use the variable enable_dns in our Terraform module. Open the file ./common_modules/vpc/main.tf and edit the vpc module by modifying these two lines:

  enable_dns_hostnames = true
  enable_dns_support = true
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It should look like this:

  enable_dns_hostnames = var.enable_dns
  enable_dns_support = var.enable_dns
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Now, if you run terragrunt apply from ./prod/us-west-2/vpc/ again you should not be prompted for variable input.

A couple of clean-up items. First, let's go back to the enable_dns variable definition and add a description and default value. Back in the ./common_modules/vpc/variables.tf update the enable_dns variable to:

variable "enable_dns" {
  type = bool
  default = true
  description = "Should DNS services be enabled." 
}
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It's a best practice to add descriptions to all your Terraform definitions, as they can be used to generate a dependency graph by running in the resource defintion folder:

terragrunt graph
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But more importantly, make sure you add a type all your variables. They are some instances where Terraform assumes a variable is a type when the input will not be compatible. That is, Terraform may assume and variable is a string, but you meant to provide it a boolean. Trust me. Declaring an appropriate type on all variables will save you a lot of time debugging Terraform code one day--not that I've ever lost a day's work to such a problem.

Last clean-up item, let's go back to the ./commond_modules/vpc/ directory and run:

terraform fmt
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This will ensure our code stays nice and tidy.

This last bit is optional, but if you've made additional changes and want to keep them, don't forget to commit them and push them to your repository:

git add .
git commit -m "Init"
git push
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Let's Destroy a VPC

Lastly, let's use Terragrunt to destroy the VPC we made. I'm often experimenting on my own AWS account and get worried I'll leave something on waking with an astronomical bill. Getting comfortable with Terragrunt has taken a lot of the fear away, as at the of the day clean up is often as easy as running terragrunt destroy.

Let's use it to destroy our VPC. And don't worry, we can redeploy it by running terragrunt apply again.

In the terminal navigate to ./prod/us-west-2/vpc/ folder and run:

terragrunt destroy
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Before you type "yes" ensure you are in the correct directory. If you are, type "yes," hit enter, and watch while Terraform destroys everything we built together.

What's Next

In the a next article we'll begin to add resources to our VPC, but we will take a break from Terraform and Terragrun and use the Serverless Framework to attach an API Gateway to our existing VPC. I'm so excited! 🙌🏽

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