How do Terraform modules work and what makes a good module?

A Terraform module is a reusable group of resource configurations. Every directory with .tf files is a module. You call modules from a root module to avoid repeating code.

What makes a good module:

• Single responsibility: One module for VPC, another for EKS, another for RDS.
• Parameterized: Accept variables to customize behavior per environment.
• Versioned: Pin module versions in the source attribute.
• Outputs: Expose useful outputs (VPC ID, subnet IDs) for other modules to consume.