A three-tier architecture consisting of a Web tier, Application tier and a Database tier in private subnets with Autoscaling for the web and application tier and a load balancer. A Bastion Host and Nat gatway provisioned to allow ssh access to the instances and access to the internet.

Terraform modules were used to make the process easily repeatable and reusable.
This deployment will create a scalable, secure and highly available infrastructure that separates the different layers ensuring they are all communicating with each other. The architecture includes an Amazon Virtual Private Cloud (VPC), Elastic Load Balancer (ELB), Auto Scaling Group (ASG), and a Relational Database(RDS).

• The Web tier will have a bastion host and NAT gateway provisioned in the public subnets. The bastion host will serve as our access point to the underlying infrastructure. The NAT Gateway will allow our private subnets to communicate with the internet while maintaining a level of security by hiding the private instances' private IP addresses from the public internet.
• In the Application tier, we will create an internet facing load balancer to direct internet traffic to an autoscaling group in the private subnets, along with a backend autoscaling group for our backend application. We will create a script to install the apache webserver in the frontend, and a script to install Node.js in the backend.
• In the Database tier, we will have another layer of private subnets hosting a MySQL database which will eventually be accessed using Node.js..

I have provided a step-by-step guide to deploying this architecture on Amazon Web Services (AWS) using Terraform.

Before you begin, ensure that you have the following prerequisites:

1. AWS account credentials (access key ID and secret access key).
2. Terraform installed on your local machine. You can download Terraform from the official website: https://www.terraform.io/downloads.html.
3. Basic knowledge of AWS services such as EC2, VPC, ELB, ASG, and RDS.
4. Familiarity with the basics of Terraform, including how to write Terraform configuration files (.tf).

Follow these step-by-step instructions to deploy a three-tier architecture on AWS using Terraform:

1. Open a terminal or command prompt on your local machine.
2. Clone the repository containing the Terraform configuration files:

   git clone https://github.com/your-repo-url.git
   

3. Change into the project directory:

   cd your-repo-directory
   

1. Open the AWS Management Console in your web browser.
2. Navigate to the IAM service.
3. Create a new IAM user or use an existing one.
4. Assign the necessary permissions to the IAM user, such as AmazonEC2FullAccess, AmazonRDSFullAccess, AmazonVPCFullAccess, and ElasticLoadBalancingFullAccess.
5. Generate an access key ID and secret access key for the IAM user.
6. Configure the AWS CLI with the IAM user credentials using the following command:

   aws configure
   

   Enter the access key ID and secret access key when prompted, and optionally set the default region.

1. Sign in to your AWS account.
2. Open the Amazon S3 service.
3. Click "Create Bucket" and configure basic settings like name and region.
4. Optionally, enable features like versioning, logging, and encryption.
5. Review settings and click "Create bucket."

1. Open the project directory in a text editor.
2. Locate the Terraform configuration file named `terraform.tfvars”.
3. Modify the values of the variables according to your requirements.
   • dbuser: Set the username for the database.
   • dbpassword: Set the password for the database.
   • db_name: Set the name of the database. Do not forget to gitignore your .tfvars file

1. In the terminal or command prompt, navigate to the project directory., cd to the root directory ‘terraform’
2. Run the following command to fix any syntax issue

   terraform fmt
   

3. Run the following command to initialize Terraform and download the required providers:

   terraform init
   

1. Run the following command to review the changes that Terraform will make:

   terraform plan
   

   Review the output to ensure that the planned infrastructure matches your expectations.

1. Run the following command to deploy the infrastructure:

   terraform apply
   

   Terraform will show you a summary of the changes that will be made. Type yes to confirm and start the deployment.

2. Wait for Terraform to provision the infrastructure. This process may take several minutes.

1. After the deployment is complete, Terraform will output the DNS name of the ELB.
2. Copy the DNS name and paste it into your web browser.
3. If everything is set up correctly, you should see the application running.

If you want to tear down the infrastructure and remove all resources created by Terraform, you can follow these steps:

1. In the terminal or command prompt, navigate to the project directory.
2. Run the following command to destroy the infrastructure:

   terraform destroy
   

   Type yes to confirm the destruction.

If you go into your AWS console, you should be able to see the VPC and subnets, internet gateway, route tables and associations, EC2 instances running in the proper locations, load balancers, and RDS database.

If we copy the load balancer endpoint we got from our Terraform output, and place it in the search bar, we will see the message we specified in our script for the Apache webserver. If we refresh the page, we should see the IP address from the other instance in our frontend autoscaling group.

Congratulations! You have successfully deployed a three-tier architecture on AWS using Terraform. This architecture provides a scalable and highly available infrastructure for your applications. Make sure to follow AWS best practices and security recommendations when deploying your production workloads.