Terraform: Autoscale with AWS ALB

These are not new concepts and I guess, no explanation required. Let us get into the matter. This setup is done for California AWS Region (us-west-1). This is a very basic setup to create autoscaling group with essential resources including Application Load Balancer.

Pre-requsite

1 - An AMI from which instance is launched can give rise web service
2 - A VPC with two public subnet (for launching ALB) and two private 
subnets (Launching EC2 instances )
3 - Security group which has public access to port 80 (for ALB), and another
 one for EC2 instance connectivity 
4 - .pem key 

Step 1: Create a terraform AWS Provider. create a provider.tf terraform code file like below

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
    }
  }
}

# Configure the AWS Provider
provider "aws" {
  region = "us-east-1"
  access_key = "Your Access Key"
  secret_key = "Your Secret Key"
}

Step 2: Create a Launch template which contains attributes for EC2 instances.

resource "aws_launch_template" "my-launch-template-1" {
  name_prefix     = "my-lt"
  image_id        = "ami-XXXXXXX"
  instance_type   = "t2.micro"
  key_name        = "Key_Name"
  tag_specifications {
    resource_type = "instance"
    tags = {
      Name = "AS-Instance"
    }
  }

  placement {
    availability_zone = "us-west-1a"
    }
  network_interfaces {
    subnet_id = "subnet-XXXXXXXX"  # Private subnet ID
    security_groups = [ "sg-XXXXXXXX" ] 
    }

  block_device_mappings {
    device_name = "/dev/xvda"
    ebs {
       volume_size = 8
        }
      }
}

Step 3: Create ALB. Use public subnets here

resource "aws_lb" "my-alb-1" {
  name               = "my-alb"
  internal           = false
  load_balancer_type = "application"
  security_groups    = [ "sg-YYYYYYYY" ]
  subnets            = ["subnet-YYYYYYY","subnet-ZZZZZZZZ"]
  enable_deletion_protection = false
  enable_cross_zone_load_balancing = true
}

Step 4: Create Target Group for the ALB

resource "aws_lb_target_group" "my-tg-1" {
  name        = "my-target-group"
  port        = 80
  protocol    = "HTTP"
  target_type = "instance"
  vpc_id      =  "vpc-XXXXXXXX"
  health_check {
   }
}

Step 5: Create a Listener and Link to the ALB. This will forward the requests to the Target Group in the code

  resource "aws_lb_listener" "my-alb-listener-1" {
  load_balancer_arn = aws_lb.my-alb-1.arn
  port              = 80
  protocol          = "HTTP"
  default_action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.my-tg-1.arn
  }
}

Step5 : Create Auto Scaling Group. Use the Private Subnet here. Include ALB Target Group

resource "aws_autoscaling_group" "my-asg-1" {
  name                  = "my-autoscaling-group"
  desired_capacity      = 1
  max_size              = 2
  min_size              = 1
  health_check_type     = "EC2"
  termination_policies  = ["OldestInstance"]
  vpc_zone_identifier   = ["subnet-XXXXXXX","subnet-BBBBBBBB"]
  target_group_arns   = [aws_lb_target_group.my-tg-1.arn]
  launch_template {
    id      = aws_launch_template.my-launch-template-1.id
    version = "$Latest"
     }
}

Step 6: Execute terraform apply command to create AWS resources.

Step 7: Now access the load balancer fro the web browser. We should be able to your web page. For me it is like below

Conclusion:

Creating a Auto scaling group with Application Load balancer is an easy process with terraform.

Disclaimer: It is recommended to do a thorough test before applying in production environment.