Provision resilient infra using terraform on AWS for hosting an nginx web application with Autoscaling in 2 zones and an Application Load Balancer

This is an example terraform project which deploys nginx web application on AWS infrastructure which is:

• isolated in VPC
• two zones hosting one subnet each
• Load balanced
• Auto scales based on CPU utilization
• EC2 instances accessible by SSH
• security for EC2 instances set to only allow http(80), icmp and ssh(22) traffic
• Load Balancer only accepts http(80) traffic

Assumptions made

1. I used the CIDR 172.1.0.0/25 for VPC
2. I provided some default values for variables in 0-variables.tf file
3. I have only AWS Free tier account, so I tested the code with EC2 instance type t2.micro
4. I split the VPC CIDR into two subnets, one subnet for one zone.
5. I used Ubuntu 20.04 for provisioning EC2 instances.

How to run

1. Gather AWS account info and install following prerequisites
   • Terraform v1.1.2
   • create an AWS account
2. Setup terraform.tfvars file with appropriate values. It should contain following 6 values:
   • AWS_ACCESS_KEY : Your AWS account access key
   • AWS_SECRET_KEY : Your AWS account secret key
   • AWS_REGION : set AWS region for provisioning infrastructure(Example: "us-east-2")
   • instance_type : set EC2 instance type to be provisioned (Example: "t2.micro")
   • PUBLIC_KEY_PATH : set path to your public rsa key so you can ssh into EC2 instances which are created by terraform (Example: "~/.ssh/mykey.pub")
   • ALLOW_CIDR : provide a cidr block of Public IPs, these IPs will be given SSH access to EC2 instances (Example: "99.145.210.10/32")
3. Run the following commands to provision infra on AWS, making sure each command executes without any errors

   cd <path/to/this/repo>
   terraform init
   terraform plan
   terraform apply

4. Output of terraform apply will print value for lb_dns_name, this is load balancer's DNS url, copy paste and hit it from browser. You will see that instance-id rotates between the two serving nginx EC2 instances.
5. Destroy the above provisioned infrastructure by running terraform destroy command.