infrastructure-terraform

What this skill does

# Infrastructure Terraform

Expert knowledge for Infrastructure as Code using Terraform with focus on declarative HCL, state management, and resilient infrastructure.

## When to Use This Skill

| Use this skill when... | Use a `tfc-*` sibling instead when... |
|---|---|
| Writing or modifying Terraform HCL configuration locally | Inspecting Terraform Cloud run state via API (`tfc-run-status`) |
| Running `terraform init/plan/apply/destroy` against a backend | Reading TFC plan/apply log streams (`tfc-run-logs`) |
| Designing module structure, providers, or remote backends | Analyzing structured plan JSON from a TFC run (`tfc-plan-json`) |
| Debugging local state, drift, or import workflows | Listing or filtering TFC run history (`tfc-list-runs`, `tfc-workspace-runs`) |

## Core Expertise

**Terraform & IaC**
- **Declarative Infrastructure**: Clean, modular, and reusable HCL code
- **State Management**: Protecting and managing Terraform state with remote backends
- **Providers & Modules**: Leveraging community and custom providers/modules
- **Execution Lifecycle**: Mastering the plan -> review -> apply workflow

## Infrastructure Provisioning Process

1. **Plan First**: Always generate `terraform plan` and review carefully before changes
2. **Modularize**: Break down infrastructure into reusable and composable modules
3. **Secure State**: Use remote backends with locking to protect state file
4. **Parameterize**: Use variables and outputs for flexible and configurable infrastructure
5. **Destroy with Caution**: Double-check plan before running `terraform destroy`

## Essential Commands

```bash
# Core workflow
terraform init                   # Initialize working directory
terraform plan                   # Generate execution plan
terraform apply                  # Apply changes
terraform destroy               # Destroy infrastructure

# State management
terraform state list            # List all resources
terraform state show <resource> # Show specific resource
terraform state pull > backup.tfstate  # Backup state

# Validation and formatting
terraform validate              # Validate configuration
terraform fmt -recursive        # Format all files recursively
terraform fmt path/to/dir       # Format specific directory
terraform graph | dot -Tsvg > graph.svg  # Dependency graph

# Working with directories (use -chdir to stay in repo root)
terraform -chdir=gcp fmt        # Format files in gcp/ directory
terraform -chdir=gcp validate   # Validate gcp/ configuration
terraform -chdir=gcp plan       # Plan from specific directory
terraform -chdir=modules/vpc init  # Init module directory

# Debugging
export TF_LOG=DEBUG             # Enable debug logging
terraform plan -out=tfplan      # Save plan for review
terraform show tfplan           # View saved plan
```

## Best Practices

**Module Structure**
```hcl
module "vpc" {
  source  = "./modules/vpc"
  version = "1.0.0"

  vpc_cidr = var.vpc_cidr
  environment = var.environment
}

output "vpc_id" {
  value = module.vpc.vpc_id
}
```

**Variable Configuration**
```hcl
variable "environment" {
  description = "Environment name"
  type        = string
  validation {
    condition     = contains(["dev", "staging", "prod"], var.environment)
    error_message = "Environment must be dev, staging, or prod."
  }
}
```

**Remote State Backend**
```hcl
terraform {
  backend "s3" {
    bucket         = "my-terraform-state"
    key            = "prod/terraform.tfstate"
    region         = "us-east-1"
    encrypt        = true
    dynamodb_table = "terraform-locks"
  }
}
```

**Provider Configuration**
```hcl
terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
  required_version = ">= 1.5"
}
```

## Key Debugging Techniques

**State Debugging**
```bash
# State inspection
terraform state list
terraform state show aws_instance.web

# State recovery
terraform refresh
terraform plan -refresh-only
terraform import aws_instance.existing i-1234567890
```

**Error Resolution**
```bash
# Provider errors
terraform init -upgrade
terraform init -reconfigure

# Resource conflicts
terraform taint aws_instance.broken
terraform apply -target=aws_instance.web
```

## Agentic Optimizations

| Context | Command |
|---------|---------|
| Format directory | `terraform -chdir=path/to/dir fmt` |
| Check format (CI) | `terraform fmt -check -recursive` |
| Validate config | `terraform -chdir=path/to/dir validate` |
| Compact plan | `terraform plan -compact-warnings` |
| JSON plan output | `terraform plan -out=plan.tfplan && terraform show -json plan.tfplan` |
| List resources | `terraform state list` |

## Quick Reference

| Flag | Description |
|------|-------------|
| `-chdir=DIR` | Change to DIR before running command |
| `-recursive` | Process directories recursively |
| `-check` | Check formatting without changes (CI) |
| `-compact-warnings` | Show warnings in compact form |
| `-json` | Output in JSON format |
| `-out=FILE` | Save plan to file |
| `-target=RESOURCE` | Target specific resource |
| `-refresh-only` | Only refresh state, no changes |

For detailed debugging patterns, advanced module design, CI/CD integration, and troubleshooting strategies, see REFERENCE.md.