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
2. AWS Region
3. Instance Type
4. Key Name
5. Define Security Groups and Associate them as a List item to AWS EC2 Instance
6. vpc-ssh
7. vpc-web
8. Learn about Terraform Output Values
9. Public IP
10. Public DNS
11. Get latest EC2 AMI ID Using Terraform Datasources concept
12. We are also going to use existing EC2 Key pair terraform-key
13. 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*