terraform-developer

name	terraform-developer
description	Develop declarative Terraform configurations. Use when the user asks to create, update, or debug Terraform code, Terraform descriptors, Terraform resources, Terraform modules, or when you need to develop Terraform code.
license	MIT

Terraform Developer

This skill provides expertise in developing Terraform configurations, descriptors, modules, resources.

Core Principles

• Prefer resources over modules: Favor simple resources for one-off configurations to keep designs flat. Introduce modules only when encapsulating complex, highly cohesive infrastructure or when reusability across multiple environments or projects is strictly required.
• Loops over resources and modules: Prefer for and for_each loops over repetitions.

Best Practices

• Terraform dependencies lockfile: Generate Terraform dependency lockfiles running terraform init, and remind the user to do so and commit the lock file. If the infrastructure is shared across different operating systems or architectures, use terraform providers lock -platform=linux_amd64 -platform=darwin_arm64 ... to ensure all necessary platforms are covered.
• Validation and formatting: Run terraform validate to check for syntax errors and issues. Run terraform fmt (or terraform fmt -recursive) to automatically fix formatting issues.
• Planning: Run terraform plan after making modifications to verify the execution plan matches the intended structural changes.
• Resource naming convention: follow these rules when naming resources.
  • Use lowercase letters and underscores (_) to separate words when naming resources. Example: server_vm, not server-vm.
  • Avoid repeating the resource type in the resource name. For example, prefer resource "aws_route_table" "public" over resource "aws_route_table" "public_route_table".
• Variable definition: follow these rules when defining variables.
  • If necessary, add a suffix to the variable name that denotes the unit. Example: _gb for gigabytes.
  • Add a description and a type when defining Terraform variables.
  • Implement variable validation if applicable. If you don't know how to validate the variable, ask the user.
• Outputs definition:
  • Store outputs in a file named outputs.tf within the module or Terraform service.
  • Don't pass input variables as outputs directly. To ensure that an output isn't evaluated until a resource is fully created, the output must reference an exported attribute of the created resource (e.g., value = google_compute_instance.web.id).

Data sources that reference variables

• When you define a variable, prefer initializing a datasource that exercises that variable and reference the datasource, instead of referencing the variable directly. This helps you validate the variable (in addition to the validation block in the variable definition), and ensures that a resource referencing the variable actually exists. For example:

  variable "google_cloud_project_id" {
    description = "Google Cloud project id"
    type        = string
  }
  
  # Prefer this
  data "google_project" "google_cloud_project" {
    project_id = var.google_cloud_project_id
  }
  
  resource "google_project_service" "google_cloud_apis_good_example" {
    for_each = toset([
      "cloudresourcemanager.googleapis.com",
      "compute.googleapis.com",
    ])
  
    disable_dependent_services = false
    disable_on_destroy         = false
    project                    = data.google_project.google_cloud_project.project_id
    service                    = each.key
  }
  
  # Over this
  resource "google_project_service" "google_cloud_apis_bad_example" {
    for_each = toset([
      "cloudresourcemanager.googleapis.com",
      "compute.googleapis.com",
    ])
  
    disable_dependent_services = false
    disable_on_destroy         = false
    project                    = var.google_cloud_project_id
    service                    = each.key
  }