terraform-baseline-builder

name

terraform-baseline-builder

description

Generate, review, and refactor Terraform modules and configurations following Equinor Terraform Baseline and HashiCorp best practices. USE FOR: create Terraform module, scaffold module, write Terraform code, review Terraform, refactor Terraform, create variables, create outputs, create resources, Terraform best practices, module structure, naming conventions, Azure Terraform module. DO NOT USE FOR: deploying infrastructure, running terraform apply/plan, CI/CD pipeline setup.

Terraform Baseline Builder

This skill helps generate, review, and refactor Terraform modules and configurations that follow the Equinor Terraform Baseline and HashiCorp official best practices.

Apply this skill whenever the user asks to write, review, scaffold, or refactor Terraform code.

---

Core Principles

All generated Terraform code MUST adhere to these principles:

• Simplicity: Module contents should be minimal and simple.
• Consistency: Follow consistent naming conventions, structure, and coding standards.
• Reusability: Design modules to be reusable across different projects and environments.
• Transparency: Purpose should be clear and well-documented.
• Predictability: Module behavior should be predictable.
• Security: Follow security best practices (e.g., Microsoft security recommendations for Azure resources).
• Maintainability: Easy to maintain with minimal technical debt.

---

Module Structure (Standard)

Every module MUST follow the HashiCorp standard module structure:

.
├── README.md
├── main.tf          # Primary entrypoint; all resource/data blocks (or nested module calls)
├── variables.tf     # All variable blocks, in alphabetical order
├── outputs.tf       # All output blocks, in alphabetical order
├── terraform.tf     # Single terraform block: required_version + required_providers
├── locals.tf        # Local values (if referenced across multiple files)
├── modules/         # Nested submodules (optional)
│   └── <submodule>/
│       ├── README.md
│       ├── main.tf
│       ├── variables.tf
│       └── outputs.tf
├── examples/        # Usage examples (optional)
│   └── <example>/
│       └── main.tf
└── test/            # Automated tests (optional)

File Rules

• main.tf is the primary entrypoint. For simple modules, all resources go here. For complex modules, split by logical group (e.g., network.tf, storage.tf, compute.tf).
• variables.tf and outputs.tf MUST exist even if empty.
• terraform.tf contains ONLY the terraform block with required_version and required_providers.
• Use a separate providers.tf only if provider configuration is complex (e.g., aliasing).
• locals.tf for local values referenced in multiple files. File-specific locals go at the top of that file.

---

Naming Conventions

Repository Naming

• Use the convention terraform-<PROVIDER>-<NAME> (e.g., terraform-azurerm-key-vault).
• For Azure modules, name after the corresponding Azure CLI group or subgroup (e.g., storage, key-vault, log-analytics).
• Separate words with - consistently.

Resource Naming

• Use descriptive nouns for resource names.
• Do NOT include the resource type in the name (the address already includes it).
• Separate words with underscores.
• Wrap resource type and name in double quotes.
• Use this as the name when a module creates a single instance of its main resource.

# BAD
resource "azurerm_storage_account" "storage_account_main" { ... }

# GOOD
resource "azurerm_storage_account" "this" { ... }

Variable and Output Naming

• Variables: <resource>_<block>_<argument> (e.g., account_replication_type)
• Outputs: <resource>_<block>_<attribute> (e.g., account_id)
• Exception: Omit the module name from variable/output names. In module storage, use account_name not storage_account_name.

---

Variables

Declaration Rules

• All resource arguments MUST be exposed as variables.
• ALWAYS include type and description for every variable.
• If the variable is optional, define a reasonable default.
• For sensitive variables, set sensitive = true.
• Prefer simple types (string, number, bool) over complex types where possible.

Parameter Order (within a variable block)

variable "example" {
  type        = string
  description = "Description of the variable."
  default     = "value"       # optional
  sensitive   = true          # optional
  nullable    = false         # optional

  validation {                # optional
    condition     = ...
    error_message = "..."
  }
}

Description Conventions

When valid values are known, append to the description:

• Exact set known: Value must be "X" or "Y".
• Range known: Value must be between X and Y.
• Subset known: Possible values include X, Y, and Z.
• Format known: Value must be in F format, e.g. X, Y, and Z.

Always add validation blocks for known value constraints:

variable "kind" {
  type        = string
  description = "The kind of Web App to create. Value must be \"Linux\" or \"Windows\"."
  default     = "Linux"

  validation {
    condition     = contains(["Linux", "Windows"], var.kind)
    error_message = "Kind must be \"Linux\" or \"Windows\"."
  }
}

---

Outputs

Declaration Rules

• All resource attributes MUST be exposed as outputs.
• ALWAYS include a description for every output.

Parameter Order (within an output block)

output "example_id" {
  description = "The ID of the example resource."
  value       = azurerm_example.this.id
  sensitive   = false  # optional
}

---

Resources

General Rules

• Configure resources based on provider security recommendations (e.g., Microsoft security recommendations for Azure).
• Use resources that do not require more than Contributor role at the resource group scope.
• Do NOT create resources that are automatically created by the provider (e.g., Azure hidden resources like the master database for SQL Server).
• A module should only perform control plane operations, not data plane operations.

Single Resource per Module

• A single module call should create a single instance of the main resource.
• A module should NOT create just a single resource unless that resource requires complex configuration.

Submodules

If a resource is a child of another resource:

• The parent resource should be a module.
• The child resource should be a submodule under modules/.
• Reference as module//modules/<child>.

Resource Parameter Order

resource "azurerm_example" "this" {
  # 1. count or for_each (meta-arguments first)
  count = var.enable ? 1 : 0

  # 2. Resource-specific non-block parameters
  name                = var.name
  resource_group_name = var.resource_group_name
  location            = var.location

  # 3. Resource-specific block parameters
  site_config {
    # ...
  }

  # 4. Lifecycle block
  lifecycle {
    prevent_destroy = true
  }

  # 5. depends_on
  depends_on = [azurerm_resource_group.this]
}

---

Conditional Resources (0 or 1)

Use count with a conditional expression based on a static value (variable or local):

variable "kind" {
  type        = string
  description = "The kind of Web App. Value must be \"Linux\" or \"Windows\"."
  default     = "Linux"

  validation {
    condition     = contains(["Linux", "Windows"], var.kind)
    error_message = "Kind must be \"Linux\" or \"Windows\"."
  }
}

resource "azurerm_linux_web_app" "this" {
  count = var.kind == "Linux" ? 1 : 0
  # ...
}

resource "azurerm_windows_web_app" "this" {
  count = var.kind == "Windows" ? 1 : 0
  # ...
}

---

Repeatable Resources (0 or more)

Use for_each with a variable of type map(object({})). Default to {} for no resources:

variable "firewall_rules" {
  description = "A map of firewall rules to create."

  type = map(object({
    name             = string
    start_ip_address = string
    end_ip_address   = string
  }))

  default = {}
}

resource "azurerm_mssql_firewall_rule" "this" {
  for_each = var.firewall_rules

  name             = each.value.name
  start_ip_address = each.value.start_ip_address
  end_ip_address   = each.value.end_ip_address
}

---

Dynamic Blocks

Repeatable Nested Blocks (0 or more)

Use list(object({})) with dynamic blocks. Default to []:

variable "auth_settings_active_directory" {
  description = "A list of Active Directory authentication settings."

  type = list(object({
    client_id                  = string
    client_secret_setting_name = string
  }))

  default = []
}

resource "azurerm_linux_web_app" "this" {
  # ...

  auth_settings {
    enabled = length(var.auth_settings_active_directory) == 0 ? false : true

    dynamic "active_directory" {
      for_each = var.auth_settings_active_directory

      content {
        client_id                  = active_directory.value["client_id"]
        client_secret_setting_name = active_directory.value["client_secret_setting_name"]
      }
    }
  }
}

Non-Repeatable Nested Blocks (0 or 1)

Use object() with a null default. Wrap in [val] or [] for the for_each:

variable "blob_properties" {
  description = "The blob properties for this storage account."

  type = object({
    versioning_enabled  = optional(bool, true)
    change_feed_enabled = optional(bool, true)
  })

  default = {}
}

resource "azurerm_storage_account" "this" {
  # ...

  dynamic "blob_properties" {
    for_each = var.blob_properties != null ? [var.blob_properties] : []

    content {
      versioning_enabled  = blob_properties.value["versioning_enabled"]
      change_feed_enabled = blob_properties.value["change_feed_enabled"]
    }
  }
}

Exceptions for non-repeatable blocks:

• Blocks defined as required by the provider (e.g., site_config on azurerm_linux_web_app).
• Blocks that are optional but have an argument to enable/disable (e.g., auth_settings with enabled).

---

Meta-Arguments

Lifecycle

• Use prevent_destroy = true on stateful resources (databases, storage) to prevent accidental data loss.
• Use ignore_changes sparingly — heavy use leads to configuration drift.

count vs for_each

• Use count for conditional creation (0 or 1) based on a boolean/string.
• Use for_each for repeatable resources where each instance needs distinct values.
• Place count or for_each as the first argument in the resource block.

---

Code Formatting and Style

• Run terraform fmt before committing.
• Run terraform validate to check syntax.
• Use # for all comments (not // or /* */).
• Indent two spaces per nesting level.
• Align = signs for consecutive single-line arguments at the same nesting level.
• Separate top-level blocks with one blank line.
• Place meta-arguments (count, for_each) first, then arguments, then nested blocks, then lifecycle, then depends_on.
• Let code "build on itself" — define data sources before the resources that reference them.

---

Version Pinning

• Pin provider versions in required_providers:

terraform {
  required_providers {
    azurerm = {
      source  = "hashicorp/azurerm"
      version = "~> 4.0"
    }
  }

  required_version = ">= 1.9"
}

• Pin module sources to a specific ref or version:

module "storage" {
  source = "github.com/equinor/terraform-azurerm-storage?ref=v12.1.1"
  # ...
}

• Use Dependabot to keep module versions up to date.

---

.gitignore

Always commit:

• All .tf files
• .terraform.lock.hcl (dependency lock file)
• .gitignore
• README.md

Never commit:

• terraform.tfstate and terraform.tfstate.*
• .terraform.tfstate.lock.info
• .terraform/ directory
• Saved plan files
• .tfvars files containing sensitive information

---

Testing

• Write automated tests for all variants of the resources using Terraform native tests (terraform test).
• Place test files in a tests/ directory with the .tftest.hcl extension.
• Run tests in CI (e.g., as a pre-merge check in pull requests).

---

Module Composition

• Keep the module tree flat — prefer one level of child modules.
• Use dependency inversion: pass dependencies as input variables rather than having modules create their own.
• Use data-only modules to encapsulate data source lookups when the retrieval method may change.

---

Security

• Configure resources based on provider security recommendations.
• Use sensitive = true for variables containing secrets.
• Never hardcode credentials — use environment variables or a secrets manager.
• Use dynamic provider credentials when possible.
• Modules should only perform control plane operations (not data plane) to avoid firewall workarounds that lower security.

---

Checklist

Before submitting Terraform code, verify:

• Follows standard module structure (main.tf, variables.tf, outputs.tf, terraform.tf)
• All arguments exposed as variables with type, description, and validation where applicable
• All attributes exposed as outputs with description
• Resource names use underscores and descriptive nouns (no resource type in the name)
• terraform fmt passes
• terraform validate passes
• prevent_destroy set on stateful resources
• Provider and module versions are pinned
• .gitignore excludes state files, .terraform/, and sensitive .tfvars
• Security recommendations followed (no hardcoded credentials, sensitive = true where needed)
• Conditional resources use count; repeatable resources use for_each with map(object({}))
• Dynamic blocks follow the correct pattern (list for repeatable, nullable object for non-repeatable)