My three-tier AWS architecture worked. VPC, subnets, bastion host, app server, RDS, all deployed and running. But my main.tf was a flat file with everything mixed together. Security groups next to route tables next to RDS instances next to IAM roles.
It worked for a learning project. It would not work in a real team environment where multiple people need to understand, maintain, and extend the infrastructure.
So I refactored it into modules. Here is what I learned.
What Is a Module
A module is just a folder with its own Terraform files. Nothing magic about it. You move related resources into that folder, define what it needs as inputs, define what it exposes as outputs, and then call it from your root configuration.
