Skip to content

Terraform Resource Meta-Argument depends_on

Step-01: Introduction

  • Create 9 aws resources in a step by step manner
  • Create Terraform Block
  • Create Provider Block
  • Create 9 Resource Blocks
  • Create VPC
  • Create Subnet
  • Create Internet Gateway
  • Create Route Table
  • Create Route in Route Table for Internet Access
  • Associate Route Table with Subnet
  • Create Security Group in the VPC with port 80, 22 as inbound open
  • Create EC2 Instance in respective new vpc, new subnet created above with a static key pair, associate Security group created earlier
  • Create Elastic IP Address and Associate to EC2 Instance
  • Use depends_on Resource Meta-Argument attribute when creating Elastic IP

Step-02: Pre-requisite - Create a EC2 Key Pair

  • Create EC2 Key pair terraform-key and download pem file and put ready for SSH login

Step-03: c1-versions.tf - Create Terraform & Provider Blocks

  • Create Terraform Block
  • Create Provider Block
# Terraform Block
terraform {
  required_version = "~> 0.14.6"
  required_providers {
    aws = { 
      source = "hashicorp/aws"
      version = "~> 3.0"
    }
  }
}

# Provider Block
provider "aws" {
  region = "us-east-1"
  profile = "default"
}

Step-04: c2-vpc.tf - Create VPC Resources

Step-04-01: Create VPC using AWS Management Console

  • Create VPC Manually and understand all the resources we are going to create. Delete that VPC and start writing the VPC template using terraform

Step-04-02: Create VPC using Terraform

  • Create VPC Resources listed below
  • Create VPC
  • Create Subnet
  • Create Internet Gateway
  • Create Route Table
  • Create Route in Route Table for Internet Access
  • Associate Route Table with Subnet
  • Create Security Group in the VPC with port 80, 22 as inbound open
# Resource Block
# Resource-1: Create VPC
resource "aws_vpc" "vpc-dev" {
  cidr_block = "10.0.0.0/16"

  tags = {
    "name" = "vpc-dev"
  }
}

# Resource-2: Create Subnets
resource "aws_subnet" "vpc-dev-public-subnet-1" {
  vpc_id = aws_vpc.vpc-dev.id
  cidr_block = "10.0.1.0/24"
  availability_zone = "us-east-1a"
  map_public_ip_on_launch = true
}


# Resource-3: Internet Gateway
resource "aws_internet_gateway" "vpc-dev-igw" {
  vpc_id = aws_vpc.vpc-dev.id
}

# Resource-4: Create Route Table
resource "aws_route_table" "vpc-dev-public-route-table" {
  vpc_id = aws_vpc.vpc-dev.id
}

# Resource-5: Create Route in Route Table for Internet Access
resource "aws_route" "vpc-dev-public-route" {
  route_table_id = aws_route_table.vpc-dev-public-route-table.id 
  destination_cidr_block = "0.0.0.0/0"
  gateway_id = aws_internet_gateway.vpc-dev-igw.id 
}


# Resource-6: Associate the Route Table with the Subnet
resource "aws_route_table_association" "vpc-dev-public-route-table-associate" {
  route_table_id = aws_route_table.vpc-dev-public-route-table.id 
  subnet_id = aws_subnet.vpc-dev-public-subnet-1.id
}

# Resource-7: Create Security Group
resource "aws_security_group" "dev-vpc-sg" {
  name = "dev-vpc-default-sg"
  vpc_id = aws_vpc.vpc-dev.id
  description = "Dev VPC Default Security Group"

  ingress {
    description = "Allow Port 22"
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  ingress {
    description = "Allow Port 80"
    from_port   = 80
    to_port     = 80
    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"]
  }

}

Step-05: c3-ec2-instance.tf - Create EC2 Instance Resource

  • Review apache-install.sh
#! /bin/bash
sudo yum update -y
sudo yum install -y httpd
sudo service httpd start  
sudo systemctl enable httpd
echo "<h1>Welcome to StackSimplify ! AWS Infra created using Terraform in us-east-1 Region</h1>" > /var/www/html/index.html
  • Create EC2 Instance Resource
# Resource-8: Create EC2 Instance
resource "aws_instance" "my-ec2-vm" {
  ami = "ami-0be2609ba883822ec" # Amazon Linux
  instance_type = "t2.micro"
  subnet_id = aws_subnet.vpc-dev-public-subnet-1.id
  key_name = "terraform-key"
    #user_data = file("apache-install.sh")
  user_data = <<-EOF
    #!/bin/bash
    sudo yum update -y
    sudo yum install httpd -y
    sudo systemctl enable httpd
    sudo systemctl start httpd
    echo "<h1>Welcome to StackSimplify ! AWS Infra created using Terraform in us-east-1 Region</h1>" > /var/www/html/index.html
    EOF  
  vpc_security_group_ids = [ aws_security_group.dev-vpc-sg.id ]
}

Step-06: c4-elastic-ip.tf - Create Elastic IP Resource

  • Create Elastic IP Resource
  • Add a Resource Meta-Argument depends_on ensuring Elastic IP gets created only after AWS Internet Gateway in a VPC is present or created
# Resource-9: Create Elastic IP
resource "aws_eip" "my-eip" {
  instance = aws_instance.my-ec2-vm.id
  vpc = true
  depends_on = [ aws_internet_gateway.vpc-dev-igw ]
}

Step-07: Execute Terraform commands to Create Resources using Terraform

# Initialize Terraform
terraform init

# Terraform Validate
terraform validate

# Terraform Plan to Verify what it is going to create / update / destroy
terraform plan

# Terraform Apply to Create EC2 Instance
terraform apply

Step-08: Verify the Resources

  • Verify VPC
  • Verify EC2 Instance
  • Verify Elastic IP
  • Review the terraform.tfstate file
  • Access Apache Webserver Static page using Elastic IP
# Access Application
http://<AWS-ELASTIC-IP>

Step-09: Destroy Terraform Resources

# Destroy Terraform Resources
terraform destroy

# Remove Terraform Files
rm -rf .terraform*
rm -rf terraform.tfstate*

References