terraform-stacks

Files (7)

• SKILL.md
• api-monitoring.md · references/
• component-blocks.md · references/
• deployment-blocks.md · references/
• examples.md · references/
• linked-stacks.md · references/
• troubleshooting.md · references/

SKILL.md (first lines)

# Terraform Stacks

Terraform Stacks simplify infrastructure provisioning and management at scale by providing a configuration layer above traditional Terraform modules. Stacks enable declarative orchestration of multiple components across environments, regions, and cloud accounts.

## Core Concepts

**Stack**: A complete unit of infrastructure composed of components and deployments that can be managed together.

**Component**: An abstraction around a Terraform module that defines infrastructure pieces. Each component specifies a source module, inputs, and providers.

**Deployment**: An instance of all components in a stack with specific input values. Use deployments for different environments (dev/staging/prod), regions, or cloud accounts.

**Stack Language**: A separate HCL-based language (not regular Terraform HCL) with distinct blocks and file extensions.

## File Structure

Terraform Stacks use specific file extensions:

- **Component configuration**: `.tfcomponent.hcl`
- **Deployment configuration**: `.tfdeploy.hcl`
- **Provider lock file**: `.terraform.lock.hcl` (generated by CLI)

All configuration files must be at the root level of the Stack repository. HCP Terraform processes all files in dependency order.

### Recommended File Organization

```
my-stack/
├── .terraform-version               # The required Terraform version for this Stack
├── variables.tfcomponent.hcl        # Variable declarations
├── providers.tfcomponent.hcl        # Provider configurations
├── components.tfcomponent.hcl       # Component definitions
├── outputs.tfcomponent.hcl          # Stack outputs
├── deployments.tfdeploy.hcl         # Deployment definitions
├── .terraform.lock.hcl              # Provider lock file (generated)
└── modules/                         # Local modules (optional - only if using local modules)
    ├── s3/
    └── compute/
```

**Note**: The `modules/` directory is only required when using local module sources. Components can reference modules from:
- Local file paths: `./modules/vpc`
- Public registry: `terraform-aws-modules/vpc/aws`
- Private registry: `app.terraform.io/<org-name>/vpc/aws`
- Git: `git::https://github.com/org/repo.git//path?ref=v1.0.0`

HCP Terraform processes all `.tfcomponent.hcl` and `.tfdeploy.hcl` files in dependency order.

## Required Terraform version (.terraform-version)

Use Terraform v1.13.x or later to access the Stacks CLI plugin and to run
terraform stacks CLI commands. Begin by adding a .terraform-version file to
your Stack's root directory to specify the Terraform version required for your
Stack. For example, the following file specifies Terraform v1.14.5:

```
1.14.5
```

## Component Configuration (.tfcomponent.hcl)

### Variable Block

Declare input variables for the Stack configuration. Variables must define a `type` field and do not support the `validation` argument.

```hcl
variable "aws_region" {
  type        = string
  description = "AWS region for deployments"
  default     = "us-west-1"
}

variable "identity_token" {
  type        = string
  description = "OIDC identity token"
  ephemeral   = true  # Does not persist to state file
}

variable "instance_count" {
  type     = number
  nullable = false
}
```

**Important**: Use `ephemeral = true` for credentials and tokens (identity tokens, API keys, passwords) to prevent them from persisting in state files. Use `stable` for longer-lived values like license keys that need to persist across runs.

### Required Providers Block

```hcl
required_providers {
  aws = {
    source  = "hashicorp/aws"
    version = "~> 6.0"
  }
  random = {
    source  = "hashicorp/random"
    version = "~> 3.5.0"
  }
}
```

### Provider Block

Provider blocks differ from traditional Terraform:

1. Support `for_each` meta-argument
2. Define aliases in the block header (not as an argument)
3. Accept configuration through a `config` block

**Single Provider Configuration:**

```hcl
provider "aws" "this" {
  config {
    region = var.aws_region
    assume_role_with_web_identity {
      role_arn           = var.role_arn
      web_identity_token = var.identity_token
    }

From hashicorp/agent-skills, MPL-2.0.

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