0.Terraform

iac writing a infra in version control scripts
terraform is agent less
terraform is declarative

in short we have to remember only 4 commands

terraform init terraform plan terraform apply -auto-approve terraform destory

Terraform is an open-source Infrastructure as Code (IaC) tool created by HashiCorp. It allows you to define, provision, and manage cloud and on-premise infrastructure using a declarative configuration language called HashiCorp Configuration Language (HCL).

🔍 What Terraform Does

Terraform automates the creation and management of your infrastructure. Instead of manually setting up servers, databases, networking, and other components, you write code that describes what you want, and Terraform does the rest.

💡 Key Concepts of Terraform

Concept	Description
Providers	These are plugins for Terraform to interact with different services (e.g., AWS, Azure, GCP, Kubernetes, etc.).
Resources	The basic building blocks like VMs, buckets, networks defined in Terraform files.
Modules	Group of resources combined into reusable components.
State	Terraform keeps track of what infrastructure it has deployed using a `.tfstate` file.
Plan	Command to preview what Terraform will do (e.g., add, change, destroy).
Apply	Executes the actual changes as per the plan.
Destroy	Tears down everything managed by Terraform.

🧱 Structure of a Terraform Project

main.tf       --> main configuration
variables.tf  --> variables used in config
outputs.tf    --> output values after apply
terraform.tfstate --> state file

⚙️ Basic Workflow

Write Configuration

provider "aws" {
  region = "us-east-1"
}
 
resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
}

Initialize Terraform
```
terraform init
```
Preview Plan
```
terraform plan
```
Apply Changes
```
terraform apply
```

if i dont want to type yes then we can use this command

terraform apply -auto-approve

Destroy Infrastructure
```
terraform destroy
```

🌐 Providers Supported by Terraform

Cloud: AWS, Azure, Google Cloud, Oracle Cloud
Container: Docker, Kubernetes
SaaS: GitHub, Datadog, Cloudflare
Others: VMware, OpenStack, etc.

📌 Real-World Use Cases

Provisioning Cloud Infrastructure: Automate AWS EC2, RDS, S3 bucket creation.
CI/CD Pipelines: Spin up environments dynamically in DevOps workflows.
Disaster Recovery: Recreate infra from code during failures.
Multi-cloud Deployment: Manage resources across AWS + GCP using same tool.
Scaling Infrastructure: Define autoscaling groups, load balancers easily.

🧠 Advantages

✅ Infrastructure as Code
✅ Idempotent (same code = same result)
✅ Version-controlled Infrastructure
✅ Reusable and Modular
✅ Supports Multi-cloud
✅ State Management

⚠️ Challenges

🔧 Managing state in teams (use remote state via S3 + DynamoDB)
🚫 Error-prone if plan is not reviewed
🔄 Terraform is declarative, but sometimes you need imperative logic (handled via count, for_each, etc.)

🎓 In Interviews / Exams

What is Terraform?

Tool for Infrastructure as Code to automate and manage cloud resources.
Difference from other tools like Ansible?

Terraform is declarative and manages infrastructure. Ansible is imperative and is more for configuration management.
What is tfstate?

File used to keep track of the current state of infrastructure.
Why use modules?

For reusability and maintainability of Terraform code.