terraform-fundamentals

# Terraform Fundamentals Skill

Master HashiCorp Configuration Language (HCL) and core Terraform concepts for building production infrastructure.

## Quick Reference

```hcl
# Block Types Overview
terraform {}     # Settings & provider requirements
provider "x" {}  # Provider configuration
resource "x" {}  # Infrastructure objects
data "x" {}      # Read external data
variable "x" {}  # Input parameters
output "x" {}    # Export values
locals {}        # Computed values
module "x" {}    # Reusable components
```

## Core Concepts

### 1. Provider Configuration
```hcl
terraform {
  required_version = ">= 1.5.0"

  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}

provider "aws" {
  region = var.aws_region

  default_tags {
    tags = {
      Environment = var.environment
      ManagedBy   = "Terraform"
    }
  }
}
```

### 2. Resource Definitions
```hcl
resource "aws_instance" "web" {
  ami           = data.aws_ami.ubuntu.id
  instance_type = var.instance_type
  subnet_id     = aws_subnet.main.id

  tags = merge(local.common_tags, {
    Name = "${var.project}-web"
  })

  lifecycle {
    create_before_destroy = true
    prevent_destroy       = var.environment == "prod"
    ignore_changes        = [tags["LastModified"]]
  }
}
```

### 3. Variables with Validation
```hcl
variable "environment" {
  type        = string
  description = "Deployment environment"

  validation {
    condition     = contains(["dev", "staging", "prod"], var.environment)
    error_message = "Must be dev, staging, or prod."
  }
}

variable "instance_config" {
  type = object({
    instance_type     = string
    volume_size       = number
    enable_monitoring = optional(bool, true)
  })

  default = {
    instance_type = "t3.micro"
    volume_size   = 20
  }
}
```

### 4. Outputs
```hcl
output "instance_id" {
  description = "EC2 instance ID"
  value       = aws_instance.web.id
}

output "connection_info" {
  description = "SSH connection det