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3-Tier

Definition of the 3-Tier Architecture:

  • Presentation Layer (Web Tier): Public-facing application servers
  • Application Layer (App Tier): Private compute layer for business logic.
  • Data Layer (DB Tier): Managed database service

This module demonstrates the 3-tier architecture using Terraform in an AWS environment by creating the following:

  • Networking Layer

    • One VPC with 3 types of subnets
      • Public - for the Web Tier
      • Private - for the App Tier
      • Databases - dedicated subnets for the RDS DB
    • The number of subnets is configurable through the parameter nr_az (number of availability zones)
    • One Internet Gateway from the whole VPC
    • One NAT gateway in first availability zone

  • The Security Groups and Security Group rules necessary to have a secure environment:

    • The security group for web tier servers accepts HTTP and HTTPS requests from everywhere as inbound and allows outbound only to application servers.
    • The security group for the application servers accepts requests from the web servers' security group as inbound and allows outbound to the DB only.
    • The security group for the RDS database accepts connections only from application servers.

  • Web Tier:

    • Create an Application Load Balancer that forwards requests received from the Internet to an auto-scaling group for the web servers.
    • Redirect HTTP requests to HTTPS
    • Create a launch template and auto-scaling group for the web servers.

  • App Tier:

    • Create an Application Load Balancer that forwards requests received from the web servers to an auto-scaling group for the application servers.
    • Create a launch template and auto-scaling group for the application servers.

  • Database Tier:

    • Create a MySQL RDS database to be used by the application servers.

This Terraform code uses:

  • modules created and maintained by Terraform community
  • a custom module for security groups, which is easier to use than the community Terraform module
  • direct AWS resources creation