Modules and Reusable Infrastructure

A module is just a directory of .tf files that other configurations can call as a unit, parameterized by input variables and exposing outputs — every Terraform configuration you've written so far has technically been the implicit "root module." The value of factoring reusable pieces into their own named modules is the same as factoring code into functions: you write the S3-bucket-with-sane-defaults pattern once, then call it from a dev environment and a prod environment with different inputs, instead of copy-pasting the resource blocks and quietly letting them drift apart over time.

You'll build a small S3-bucket module with typed variables, validation rules, and useful outputs, then call it twice — once for a dev environment, once for prod — with different configurations, demonstrating the core pattern behind almost every real Terraform codebase's structure.