Terraform Module Library

This skill provides standardized patterns and best practices for creating and using Terraform modules.

When to Use

• Creating new reusable Terraform modules

• Refactoring existing Terraform code into modules

• Standardizing infrastructure patterns across the project

• implement specific infrastructure components (VPC, GKE, RDS, etc.) using best practices

Module Structure

Standard directory structure for a Terraform module:

module-name/ ├── main.tf # Primary logic and resources ├── variables.tf # Input variable definitions ├── outputs.tf # Output value definitions ├── versions.tf # Provider and Terraform version constraints ├── README.md # Module documentation └── examples/ # Example configurations └── complete/ # Full example usage

Best Practices

Cloud Providers

Google Cloud Platform (GCP)

• Use google-beta provider for beta features if necessary, but prefer GA.

• Follow Google's "Cloud Foundation Toolkit" patterns where applicable.

• Resource naming: Use standardized prefixes/suffixes (e.g., gcp-vpc-{env} ).

AWS

• Use standard aws provider resources.

• Tag all resources with consistent tags (Owner, Environment, Project).

General

• Version Pinning: Always pin provider and Terraform versions in versions.tf .

• Variables: Include description and type for all variables. Use validation blocks for constraints.

• Outputs: Document all outputs.

• State: Do not include backend configuration in modules; state is managed by the root configuration.

Common Module Patterns

Private Module Registry

If using a private registry, ensure source paths follow the registry's convention.

Local Modules

For local development or monorepos:

module "network" { source = "./modules/network"

...

}

Review Checklist

• Does the module have a README.md with input/output documentation?

• Are all variables typed and described?

• Are resource names deterministic or correctly scoped?

• Does it include examples/ ?

• Is terraform_remote_state avoided within the module?