This is in continuation of the 1st article - Query data sources using state file in Terraform - 1, where we have configured VPC Infrastructure.

In this article, I am going to deploy application infrastructure defined by a separate Terraform configuration and use the terraform_remote_state data source to query information about your VPC.

Finally, you will use the aws_ami data source to configure the correct AMI for the current region.

Please visit my GitHub Repository for Terraform articles on various topics being updated on constant basis.

Let’s get started!

Objectives:

1. Create infrastructure for application block

2. Change to the Application directory and Run terraform init to initialize Terraform.

3. Configure Terraform remote state

4. Scale EC2 instances

5. Configure region-specific AMIs

6. Configure EC2 subnet and security groups

7. Run terraform apply to apply the configuration

Pre-requisites:

AWS user account with admin access, not a root account.
Cloud9 IDE with AWS CLI.

Resources Used:

Terraform documentation for AMI.

data source for pulling in an AMI ID.

Steps for implementation to this project:

1. Create infrastructure for application block

Let’s create the following organizational structure as shown below.
Create a directory - terraform-data-sources-app
Create 4 files - terraform.tf, main.tf, variables.tf, outputs.tf file.

Create a terraform.tf file.

# terraform-data-sources-app/terraform.tf
# PROVIDERS BLOCK
terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.23"
    }
  }
  required_version = ">= 1.2.0"
}

Create a main.tf file.

# terraform-data-sources-app/main.tf
# Application BLOCK
provider "aws" {
  region = "us-east-1"
}

resource "random_string" "lb_id" {
  length  = 3
  special = false
}

module "elb_http" {
  source  = "terraform-aws-modules/elb/aws"
  version = "4.0.0"

  # Ensure load balancer name is unique
  name = "lb-${random_string.lb_id.result}-data-sources"

  internal = false

  security_groups = []
  subnets         = []

  number_of_instances = length(aws_instance.app)
  instances           = aws_instance.app.*.id

  listener = [{
    instance_port     = "80"
    instance_protocol = "HTTP"
    lb_port           = "80"
    lb_protocol       = "HTTP"
  }]

  health_check = {
    target              = "HTTP:80/index.html"
    interval            = 10
    healthy_threshold   = 3
    unhealthy_threshold = 10
    timeout             = 5
  }
}


resource "aws_instance" "app" {
  ami = "ami-0b5eea76982371e91"

  instance_type = var.instance_type

  subnet_id              = ""
  vpc_security_group_ids = []

  user_data = <<-EOF
    #!/bin/bash
    sudo yum update -y
    sudo yum install httpd -y
    sudo systemctl enable httpd
    sudo systemctl start httpd
    echo "<html><body><div>Welcome to Data Sources Infrastructure!</div></body></html>" > /var/www/html/index.html
    EOF
}

Create a variables.tf file.

# terraform-data-sources-app/variables.tf
# VARIABLES BLOCK
variable "instances_per_subnet" {
  description = "Number of EC2 instances in each private subnet"
  type        = number
  default     = 2
}

variable "instance_type" {
  description = "Type of EC2 instance to use"
  type        = string
  default     = "t2.micro"
}

Create an outputs.tf file.

# terraform-data-sources-app/outputs.tf
# OUTPUTS BLOCK
output "lb_url" {
  description = "URL of load balancer"
  value       = "http://${module.elb_http.elb_dns_name}/"
}

output "web_instance_count" {
  description = "Number of EC2 instances"
  value       = length(aws_instance.app)
}

2. Change to the Application directory and run `terraform init`

cd ../terraform-data-sources-app

Run terraform init to initialize Terraform.

3. Configure Terraform remote state

Like the VPC block, this configuration includes hard-coded values for the us-east-1 region. You can use the terraform_remote_state data source to use another Terraform workspace's output data.
Add a terraform_remote_state data source to the main.tf file inside the terraform-data-sources-app directory, replacing YOUR_ORG with your own Terraform Cloud organization name.
This remote state block uses the local backend to load state data from the path in the config section.

# terraform-data-sources-app/main.tf
data "terraform_remote_state" "vpc" {
  backend = "local"

  config = {
    path = "../terraform-data-sources-vpc/terraform.tfstate"
  }
}

Now, update your aws provider configuration in main.tf to use the same region as the VPC configuration instead of a hardcoded region.

# terraform-data-sources-app/main.tf
provider "aws" {
  # region = "us-east-1"
  region = data.terraform_remote_state.vpc.outputs.aws_region
}

The VPC configuration also included outputs for subnet and security group IDs. Configure the load balancer security group and subnet arguments for the elb module with those values.

# terraform-data-sources-app/main.tf

module "elb_http" {
###...
  /*
  security_groups = []
  subnets         = []
  */

  security_groups = data.terraform_remote_state.vpc.outputs.lb_security_group_ids
  subnets         = data.terraform_remote_state.vpc.outputs.public_subnet_ids
###...
}

4. Scale EC2 instances

You can use values from data sources just like any other Terraform values, including by passing them to functions.
The configuration in main.tf only uses a single EC2 instance.
Update the configuration to use the instances_per_subnet variable to provision multiple EC2 instances per subnet.

# terraform-data-sources-app/main.tf

resource "aws_instance" "app" {
###...
  count = var.instances_per_subnet * length(data.terraform_remote_state.vpc.outputs.private_subnet_ids)

  ami = "ami-0b5eea76982371e91"
###...
}

Now when you apply this configuration, Terraform will provision var.instances_per_subnet instances for each private subnet configured in your VPC workspace.

5. Configure region-specific AMIs

The AWS instance configuration also uses a hard-coded AMI ID, which is only valid for the us-east-1 region.
Use an aws_ami data source to load the correct AMI ID for the current region.
Add the following to main.tf.

# terraform-data-sources-app/main.tf
data "aws_ami" "amazon_linux" {
  most_recent = true
  owners      = ["amazon"]

  filter {
    name   = "name"
    values = ["amzn2-ami-hvm-*-x86_64-gp2"]
  }
}

Replace the hard-coded AMI ID with the one loaded from the new data source.

# terraform-data-sources-app/main.tf

resource "aws_instance" "app" {
  count = var.instances_per_subnet * length(data.terraform_remote_state.vpc.outputs.private_subnet_ids)

  /*
  ami = "ami-0b5eea76982371e91"
  */
  ami = data.aws_ami.amazon_linux.id

###...
}

6. Configure EC2 subnet and security groups

Finally, update the EC2 instance configuration to use the subnet and security group configuration from the VPC block.

# terraform-data-sources-app/main.tf

resource "aws_instance" "app" {
###...

  /*
  subnet_id              = ""
  vpc_security_group_ids = []
  */

  subnet_id              = data.terraform_remote_state.vpc.outputs.private_subnet_ids[count.index % length(data.terraform_remote_state.vpc.outputs.private_subnet_ids)]
  vpc_security_group_ids = data.terraform_remote_state.vpc.outputs.app_security_group_ids

###...
}

7. Run `terraform apply` to apply the application infrastructure

Run terraform apply to apply the configuration and type yes when prompted.

After a few minutes, the load balancer health checks will pass, and will return this response.
Wait for 4-5 minutes for the load balancer to be active
run this

curl $(terraform output -raw lb_url)

Copy and paste the lb_url onto a browswer

http://lb-Dju-data-sources-551760788.us-west-1.elb.amazonaws.com/

You will this successful message

Cleanup

You must destroy the application infrastructure before the VPC infrastructure.
Since the resources in the application infrastructure depend on those in the VPC infrastructure, the AWS API will return an error if you destroy the VPC first.
destroy the application infrastructure, prompt with yes.

terraform destroy

Now, change to the VPC directory.

cd ../terraform-data-sources-vpc

Destroy this VPC infrastructure as well, prompted with yes.

terraform destroy -var aws_region=us-west-1

What we have done so far

We have successfully demonstrated how to use data sources to make your configuration more dynamic.
We deployed two separate configurations for your network (VPC) and application resources and used the terraform_remote_state data source to share data between them.
We also replaced region-specific configuration with dynamic values from AWS provider data sources.

Blog

Query data sources using state file in Terraform - 2

Revathi Joshi

Objectives:

Pre-requisites:

Resources Used:

Steps for implementation to this project:

1. Create infrastructure for application block

2. Change to the Application directory and run `terraform init`

3. Configure Terraform remote state

4. Scale EC2 instances

5. Configure region-specific AMIs

6. Configure EC2 subnet and security groups

7. Run `terraform apply` to apply the application infrastructure

Cleanup

What we have done so far

Join Our Newsletter. No Spam, Only the good stuff.

Related

Query data sources using state file in Terraform - 2

Revathi Joshi

Objectives:

Pre-requisites:

Resources Used:

Steps for implementation to this project:

1. Create infrastructure for application block

2. Change to the Application directory and run terraform init

3. Configure Terraform remote state

4. Scale EC2 instances

5. Configure region-specific AMIs

6. Configure EC2 subnet and security groups

7. Run terraform apply to apply the application infrastructure

Cleanup

What we have done so far

Join Our Newsletter. No Spam, Only the good stuff.

Related

2. Change to the Application directory and run `terraform init`

7. Run `terraform apply` to apply the application infrastructure