Deploying a Highly Available Web App on AWS Using Terraform

In today’s cloud-centric world, scalability, reliability, and automation are key to maintaining robust web applications. Terraform, an infrastructure-as-code (IaC) tool, simplifies deploying complex infrastructure setups. This will guide you through deploying a clustered web server on AWS with Terraform, incorporating Auto Scaling and an Application Load Balancer (ALB) for enhanced performance and high availability.

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What You'll Learn

1. Set up an Auto Scaling Group (ASG) for managing server instances.
2. Configure an Application Load Balancer to distribute traffic.
3. Use a Launch Template for consistent instance provisioning.
4. Test the deployment by simulating scaling behaviour.

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Step 1: Key Components of the Architecture

• AWS Launch Template: Defines the AMI, instance type, and configuration for new instances.
• Auto Scaling Group (ASG): Manages the desired number of instances and adjusts capacity based on demand.
• Application Load Balancer (ALB): Distributes incoming traffic evenly across the instances.
• Security Group: Manages inbound and outbound traffic for your instances.

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Step 2: Terraform Script Overview

Below is the Terraform configuration file to set up the infrastructure: main.tf

provider "aws" {
  region = "us-east-1"
}

# Variable for SSH Key
variable "key_name" {
  description = "Key pair for SSH access" #key_name is confidential
}

# Security Group for Web Server
resource "aws_security_group" "web_sg" {
  name        = "web_sg"
  description = "Allow HTTP and SSH"

  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

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

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

# Launch Template for Auto Scaling Group
resource "aws_launch_template" "web_launch_template" {
  name          = "web-server-template"
  image_id      = "ami-0453ec754f44f9a4a" # Amazon Linux 2
  instance_type = "t2.micro"
  key_name      = var.key_name

   user_data = base64encode(<<-EOF
              #!/bin/bash
              sudo yum update -y
              sudo yum install -y httpd
              sudo systemctl start httpd
              sudo systemctl enable httpd
              echo "Hello from Server $(hostname)" > /var/www/html/index.html
              EOF
  )

  network_interfaces {
    security_groups = ["sg-0fd8d2cfa6f3af754"]
  }

  tag_specifications {
    resource_type = "instance"
    tags = {
      Name = "web-server"
    }
  }
}

# Auto Scaling Group
resource "aws_autoscaling_group" "web_asg" {
  desired_capacity     = 2
  max_size             = 5
  min_size             = 1
  launch_template {
    id      = aws_launch_template.web_launch_template.id
    version = "$Latest"
  }

  vpc_zone_identifier = ["subnet-036596d61d8685f5a", "subnet-08a1646c47df46597"] # Replace with your subnets

  target_group_arns = [aws_lb_target_group.web_lb_tg.arn]

  tag {
    key                 = "Name"
    value               = "web-server-asg"
    propagate_at_launch = true
  }
}

# Application Load Balancer
resource "aws_lb" "web_lb" {
  name               = "web-cluster-lb"
  internal           = false
  load_balancer_type = "application"
  security_groups    = [aws_security_group.web_sg.id]
  subnets            = ["subnet-036596d61d8685f5a", "subnet-08a1646c47df46597"] # Replace with your subnets

  enable_deletion_protection = false
}

# Target Group
resource "aws_lb_target_group" "web_lb_tg" {
  name        = "web-target-group"
  port        = 80
  protocol    = "HTTP"
  vpc_id      = "vpc-06c4398e7067f32b4" # Replace with your VPC ID
  target_type = "instance"

  health_check {
    path                = "/"
    interval            = 30
    timeout             = 5
    healthy_threshold   = 2
    unhealthy_threshold = 2
    matcher             = "200"
  }
}

# Listener for Load Balancer
resource "aws_lb_listener" "web_lb_listener" {
  load_balancer_arn = aws_lb.web_lb.arn
  port              = 80
  protocol          = "HTTP"

  default_action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.web_lb_tg.arn
  }
}

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Step 3: Deploying the Infrastructure

1. Initialize Terraform:

   terraform init

1. Review the Plan:

   terraform plan

• Check for potential changes and resource creation.

1. Apply the Configuration:

   terraform apply

• Confirm the action by typing your key_value and yes.

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Step 4: Verifying the Deployment

1. Load Balancer:

• Find the DNS Name of the ALB in the AWS Console and open it in your browser.
• You should see: "Hello from Server <hostname>".

1. Auto Scaling:

• Test scaling by adjusting the desired_capacity in the Auto Scaling Group and reapplying Terraform:
  

   desired_capacity = 3
  

Before scaling

After Scaling

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Conclusion

By leveraging Terraform, you’ve created a scalable and robust web server deployment. The Auto Scaling Group ensures high availability, while the Load Balancer distributes traffic efficiently. This setup serves as a strong foundation for more advanced infrastructure automation.

Have you tried deploying an Auto Scaling web server? Share your thoughts and experiences in the comments!