Managing High-Traffic Applications with AWS Elastic Load Balancer and Terraform

Handling high traffic apps is a critical difficulty in cloud infrastructure management. Whether you're running a popular website or a resource-intensive web application, making sure your infrastructure can expand and respond to changing demand is critical. Today, we'll look at how to handle high-traffic apps successfully with AWS Elastic Load Balancer (ALB) and Terraform.

Why High-Traffic Management is Critical

For any online site that receives a high volume of traffic, just installing a load balancer is insufficient. Without adequate traffic management, performance bottlenecks, sluggish response times, and downtime can develop, resulting in a negative user experience and lost income.

The key to handling high-traffic apps is to scale and distribute the load. Using AWS's effective Elastic Load Balancer (ALB), you can spread incoming application traffic over numerous servers, while Terraform automates and manages the infrastructure as code.

What Is AWS Elastic Load Balancer (ALB)?

AWS Elastic Load Balancer (ALB) distributes inbound application traffic to numerous destinations, such as EC2 instances, containers, or IP addresses. This guarantees that your traffic is balanced and no single server is overburdened with too many requests. ALBs also include capabilities such as SSL termination, WebSocket support, and automated scaling, making them indispensable for managing enormous amounts of traffic.

Scaling with AWS Elastic Load Balancer and Terraform

Step 1: Create a VPC and Subnets

The first step is to create a VPC (Virtual Private Cloud) with the necessary subnets to support your application’s infrastructure. High-traffic applications require both public and private subnets to safely handle incoming and outgoing traffic.

resource "aws_vpc" "vpc" {
  cidr_block = var.cidr_block
  instance_tenancy = "default"
  tags = {
    Name = "high-traffic-vpc"
  }
}

resource "aws_subnet" "public_subnet" {
  vpc_id = aws_vpc.vpc.id
  cidr_block = var.public_subnet_cidr
  map_public_ip_on_launch = true
  availability_zone = var.availability_zone
  tags = {
    Name = "public-subnet"
  }
}

resource "aws_subnet" "private_subnet" {
  vpc_id = aws_vpc.vpc.id
  cidr_block = var.private_subnet_cidr
  map_public_ip_on_launch = false
  availability_zone = var.availability_zone
  tags = {
    Name = "private-subnet"
  }
}

Step 2: Set Up Elastic Load Balancer (ALB)

Once your network infrastructure is set, the next step is to create an Application Load Balancer (ALB) to distribute incoming traffic across your instances. The ALB automatically scales depending on the volume of traffic, ensuring that it can handle high loads.

resource "aws_lb" "alb" {
  name               = "app-load-balancer"
  internal           = false
  load_balancer_type = "application"
  security_groups    = [aws_security_group.alb_sg.id]
  subnets            = [aws_subnet.public_subnet.id]
}

resource "aws_lb_target_group" "target_group" {
  name        = "app-target-group"
  port        = 80
  protocol    = "HTTP"
  vpc_id      = aws_vpc.vpc.id
  health_check {
    path                = "/"
    interval            = 30
    timeout             = 5
    healthy_threshold   = 3
    unhealthy_threshold = 3
  }
}

Step 3: Create Autoscaling Groups for Your EC2 Instances

To scale the application based on traffic, you'll need Auto Scaling Groups (ASGs). ASGs automatically increase or decrease the number of instances based on traffic conditions, which ensures that your infrastructure is always optimized for the load.

resource "aws_autoscaling_group" "web_asg" {
  desired_capacity = 3
  max_size         = 5
  min_size         = 2
  health_check_type = "ELB"
  target_group_arns = [aws_lb_target_group.target_group.arn]
  vpc_zone_identifier = [aws_subnet.private_subnet.id]
  launch_configuration = aws_launch_configuration.web_server.id
}

By connecting the ALB to your EC2 instances through an auto-scaling group, your application can handle growing load by automatically adding extra EC2 instances to the pool. The ALB then directs traffic to the healthy instances in the group.

Step 5: Secure Your Application

Ensure that your application is secure by adding appropriate security groups. The security group for ALB should allow traffic on port 80 (HTTP), and you can configure the security group for the instances to only allow inbound traffic from the load balancer.

resource "aws_security_group" "alb_sg" {
  description = "Allow HTTP traffic"
  vpc_id      = aws_vpc.vpc.id
  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_security_group" "app_instance_sg" {
  name        = "app-instance-sg"
  description = "Allow traffic from ALB only"
  vpc_id      = aws_vpc.vpc.id

  # Allow inbound traffic from ALB on port 80 (HTTP)
  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    security_groups = [aws_security_group.alb_sg.id]  # Only allow traffic from the ALB security group
  }

  # Allow all outbound traffic (you can customize this based on your requirements)
  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

  tags = {
    Name = "app-instance-sg"
  }
}

Terraform State and Remote Backends for Scalability

When you scale your infrastructure, the Terraform state file becomes even more critical. Managing Terraform state remotely (e.g., in S3 or Terraform Cloud) helps ensure that your infrastructure remains consistent across environments and teams. For example, using S3 with state locking via DynamoDB can prevent race conditions when scaling infrastructure.

terraform {
  backend "s3" {
    bucket = "my-terraform-state"
    key    = "terraform.tfstate"
    region = "us-east-1"
    dynamodb_table = "my-lock-table"
    encrypt = true
  }
}