Terraform Variables and Datasources

Step-00: Pre-requisite Note

• Create a terraform-key in AWS EC2 Key pairs which we will reference in our EC2 Instance

Step-01: Introduction

Terraform Concepts

• Terraform Input Variables
• Terraform Datasources
• Terraform Output Values

What are we going to learn ?

1. Learn about Terraform Input Variable basics

• AWS Region
• Instance Type
• Key Name

2. Define Security Groups and Associate them as a List item to AWS EC2 Instance

• vpc-ssh
• vpc-web

3. Learn about Terraform Output Values

• Public IP
• Public DNS

4. Get latest EC2 AMI ID Using Terraform Datasources concept
5. We are also going to use existing EC2 Key pair terraform-key
6. Use all the above to create an EC2 Instance in default VPC

Step-02: c2-variables.tf - Define Input Variables in Terraform

• Terraform Input Variables
• Terraform Input Variable Usage - 10 different types

# AWS Region
variable "aws_region" {
  description = "Region in which AWS Resources to be created"
  type = string
  default = "us-east-1"  
}

# AWS EC2 Instance Type
variable "instance_type" {
  description = "EC2 Instance Type"
  type = string
  default = "t3.micro"  
}

# AWS EC2 Instance Key Pair
variable "instance_keypair" {
  description = "AWS EC2 Key pair that need to be associated with EC2 Instance"
  type = string
  default = "terraform-key"
}

• Reference the variables in respective .tffies

# c1-versions.tf
region  = var.aws_region

# c5-ec2instance.tf
instance_type = var.instance_type
key_name = var.instance_keypair  

Step-03: c3-ec2securitygroups.tf - Define Security Group Resources in Terraform

• Resource: aws_security_group

# Create Security Group - SSH Traffic
resource "aws_security_group" "vpc-ssh" {
  name        = "vpc-ssh"
  description = "Dev VPC SSH"
  ingress {
    description = "Allow Port 22"
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
  egress {
    description = "Allow all ip and ports outboun"
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

# Create Security Group - Web Traffic
resource "aws_security_group" "vpc-web" {
  name        = "vpc-web"
  description = "Dev VPC web"
  ingress {
    description = "Allow Port 80"
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  ingress {
    description = "Allow Port 443"
    from_port   = 443
    to_port     = 443
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  egress {
    description = "Allow all ip and ports outbound"
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

• Reference the security groups in c5-ec2instance.tf file as a list item

# List Item
vpc_security_group_ids = [aws_security_group.vpc-ssh.id, aws_security_group.vpc-web.id]  

Step-04: c4-ami-datasource.tf - Define Get Latest AMI ID for Amazon Linux2 OS

• Data Source: aws_ami

# Get latest AMI ID for Amazon Linux2 OS
# Get Latest AWS AMI ID for Amazon2 Linux
data "aws_ami" "amzlinux2" {
  most_recent = true
  owners = [ "amazon" ]
  filter {
    name = "name"
    values = [ "amzn2-ami-hvm-*-gp2" ]
  }
  filter {
    name = "root-device-type"
    values = [ "ebs" ]
  }
  filter {
    name = "virtualization-type"
    values = [ "hvm" ]
  }
  filter {
    name = "architecture"
    values = [ "x86_64" ]
  }
}

• Reference the datasource in c5-ec2instance.tf file

# Reference Datasource to get the latest AMI ID
ami = data.aws_ami.amzlinux2.id 

Step-05: c5-ec2instance.tf - Define EC2 Instance Resource

• Resource: aws_instance

# EC2 Instance
resource "aws_instance" "myec2vm" {
  ami = data.aws_ami.amzlinux2.id 
  instance_type = var.instance_type
  user_data = file("${path.module}/app1-install.sh")
  key_name = var.instance_keypair
  vpc_security_group_ids = [aws_security_group.vpc-ssh.id, aws_security_group.vpc-web.id]  
  tags = {
    "Name" = "EC2 Demo 2"
  }
}

Step-06: c6-outputs.tf - Define Output Values

• Output Values

# Terraform Output Values
output "instance_publicip" {
  description = "EC2 Instance Public IP"
  value = aws_instance.myec2vm.public_ip
}

output "instance_publicdns" {
  description = "EC2 Instance Public DNS"
  value = aws_instance.myec2vm.public_dns
}

Step-07: Execute Terraform Commands

# Terraform Initialize
terraform init
Observation:
1) Initialized Local Backend
2) Downloaded the provider plugins (initialized plugins)
3) Review the folder structure ".terraform folder"

# Terraform Validate
terraform validate
Observation:
1) If any changes to files, those will come as printed in stdout (those file names will be printed in CLI)

# Terraform Plan
terraform plan
Observation:
1) Verify the latest AMI ID picked and displayed in plan
2) Verify the number of resources that going to get created
3) Verify the variable replacements worked as expected

# Terraform Apply
terraform apply 
[or]
terraform apply -auto-approve
Observations:
1) Create resources on cloud
2) Created terraform.tfstate file when you run the terraform apply command
3) Verify the EC2 Instance AMI ID which got created

Step-08: Access Application

# Access index.html
http://<PUBLIC-IP>/index.html
http://<PUBLIC-IP>/app1/index.html

# Access metadata.html
http://<PUBLIC-IP>/app1/metadata.html

Step-09: Clean-Up

# Terraform Destroy
terraform plan -destroy  # You can view destroy plan using this command
terraform destroy

# Clean-Up Files
rm -rf .terraform*
rm -rf terraform.tfstate*