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⚙️ Terraform Quick Guide

Terraform is an open-source tool for provisioning and managing infrastructure as code (IaC). It enables you to define cloud and on-prem resources using a declarative configuration language called HCL (HashiCorp Configuration Language).

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🧱 Core Concepts

• Providers: Interfaces to platforms (AWS, GCP, Azure, etc.)
• Resources: Infrastructure elements like servers, databases, etc.
• Modules: Reusable containers for Terraform code
• State: A snapshot of your current infrastructure
• Plan: Preview of what Terraform will change
• Apply: Makes the desired changes in infrastructure
• Destroy: Tears down all managed resources

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📁 Typical Project Structure

.
├── main.tf        # Main config
├── variables.tf   # Input variables
├── outputs.tf     # Output values
├── terraform.tfvars  # Default values for variables

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🚀 Basic Workflow

# 1. Initialize project (download provider plugins)
terraform init

# 2. Preview changes
terraform plan

# 3. Apply changes
terraform apply

# 4. Destroy infrastructure
terraform destroy

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🧾 Example: Provisioning an AWS EC2 Instance

provider "aws" {
  region = "us-east-1"
}

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"

  tags = {
    Name = "MyInstance"
  }
}

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📥 Input Variables

Define variables in variables.tf:

variable "region" {
  description = "AWS region"
  default     = "us-east-1"
}

Use them in config:

provider "aws" {
  region = var.region
}

Pass them with terraform.tfvars:

region = "us-west-2"

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📤 Output Values

Define outputs in outputs.tf:

output "instance_id" {
  value = aws_instance.example.id
}

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🗂 Remote State (Example with S3)

terraform {
  backend "s3" {
    bucket = "my-tf-state-bucket"
    key    = "state.tfstate"
    region = "us-east-1"
  }
}

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🔐 Best Practices

• Use version control for all Terraform code.
• Always use terraform plan before apply.
• Store state securely (use remote state + state locking).
• Use modules for reusable infrastructure.
• Use terraform fmt to format code.
• Protect sensitive variables with sensitive = true.

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🧩 Useful Commands

terraform validate     # Validate syntax
terraform fmt          # Format code
terraform output       # Show outputs
terraform taint        # Force resource recreation
terraform show         # Show current state
terraform graph        # Generate a dependency graph

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