Managing High Traffic Applications with AWS Elastic Load Balancer and Terraform

Deploys a highly available web application on AWS using an Application Load Balancer (ALB) and Auto Scaling Group (ASG). Each EC2 instance serves a static HTML page via a lightweight Python HTTP server.

Architecture

Internet
    │
    ▼
[ALB] (port 80)
    │
    ├── EC2 Instance (port 8080)
    ├── EC2 Instance (port 8080)
    └── EC2 Instance (port 8080)  ← scales between 2–10

Resources provisioned:

• aws_security_group — separate security groups for the ALB and EC2 instances (instances only accept traffic from the ALB)
• aws_launch_template — latest Amazon Linux 2 AMI, bootstrapped with a user-data script that serves an HTML page
• aws_autoscaling_group — rolling instance refresh, ELB health checks, spread across all default VPC subnets
• aws_lb — internet-facing Application Load Balancer
• aws_lb_target_group — HTTP health checks against /
• aws_lb_listener — forwards port 80 traffic to the target group

State is stored remotely in S3 (day6-terraform-state-bucket) with DynamoDB locking (terraform-state-locks) in eu-west-2.

Prerequisites

• Terraform >= 1.0
• AWS credentials configured (environment variables, ~/.aws/credentials, or IAM role)
• An S3 bucket named day6-terraform-state-bucket and a DynamoDB table named terraform-state-locks already exist in eu-west-2

Usage

# Initialise (downloads providers and configures the S3 backend)
terraform init

# Preview changes
terraform plan

# Apply
terraform apply

# Destroy all resources
terraform destroy

After a successful apply, the ALB DNS name is printed as an output. Open it in a browser to reach the web cluster.

Variables

Name	Description	Default
server_port	Port the web server listens on	8080
alb_port	Port the ALB listener accepts traffic on	80
instance_type	EC2 instance type	t2.micro
asg_min_size	Minimum instances in the ASG	2
desired_size	Desired instances in the ASG	5
asg_max_size	Maximum instances in the ASG	10

Override any variable at apply time:

terraform apply -var="instance_type=t3.small" -var="desired_size=3"

Outputs

Name	Description
alb_dns_name	DNS name of the Application Load Balancer

Remote State

Setting	Value
Backend	S3
Bucket	day6-terraform-state-bucket
Key	global/s3/terraform.tfstate
Region	eu-west-2
Locking	DynamoDB — terraform-state-locks
Encryption	Enabled