Generate High-Quality Terraform Modules

This skill writes high-quality, reusable Terraform modules following HashiCorp's official guidelines, favoring composition over inheritance. The standard module structure is main.tf (primary resources), variables.tf (input variables), outputs.tf (output values), versions.tf (provider requirements), a README.md, and an examples/ directory with working usage scenarios. Input-variable design covers descriptive names and descriptions, typed variables with object({...}) grouping related settings and optional(bool, true) defaults, and validation blocks such as checking a VPC CIDR block is valid via can(cidrhost(var.vpc_config.cidr_block, 0)).

Resource naming and tagging conventions use a local.name_prefix falling back to the project name, and a local.common_tags built by merging user-supplied tags with fixed ManagedBy/Module tags. Advanced patterns favor for_each over count for conditional resources and better state management - shown creating private subnets from a map built with { for idx, subnet in var.private_subnets : idx => subnet } - alongside count for simple boolean-gated resources like an internet gateway. Data-source lookups keep modules environment-agnostic, such as querying aws_availability_zones with an opt-in-status filter and falling back to a slice() of the discovered zones when none are explicitly configured. Output design provides both individual values (vpc_id, vpc_arn) and collections (a for expression producing private_subnet_ids, and a map of full private-subnet details) so modules compose cleanly. Provider configuration always pins version constraints in versions.tf:

terraform {
  required_version = ">= 1.0"
  
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = ">= 5.0"
    }
  }
}

Testing and validation guidance covers validation blocks on critical inputs (e.g., restricting an environment variable to dev/staging/prod), meaningful examples in the examples/ directory, and lifecycle { prevent_destroy = true } to guard against accidental deletion. Documentation best practices call for a comprehensive README covering all variables, outputs, and requirements, with multiple usage scenarios and provider-configuration examples. The five qualities every module should have: composable, configurable, consistent, documented, and tested.

Use it when authoring or reviewing a reusable Terraform module targeting a modern Terraform baseline (required_version >= 1.0) and the hashicorp/aws provider at >= 5.0 - structuring files, designing typed and validated input variables, choosing between count and for_each, or pinning provider versions. It is not a guide to Terraform state-backend setup or CI/CD pipeline configuration - it is scoped to the module's own code and structure.

Given an infrastructure component to modularize, it produces both simple count-gated resources - such as an aws_internet_gateway created only if var.enable_internet_gateway ? 1 : 0 - and for_each-driven resource sets like the private subnets, alongside typed and validated input variables and a pinned versions.tf.

Written in HCL for Terraform, with examples targeting the hashicorp/aws provider.

Infrastructure and platform engineers writing or reviewing reusable Terraform modules.