Terraform Blocks

Resources

• Defined using resource keyword, a type (e.g., google_storage_bucket), and a name (e.g., example-bucket).
• Contain arguments like name and location.

resource "google_storage_bucket" "example" {
  name     = "my-bucket"
  location = "US"
}

Data

• References an existing resource within the providers

data "aws_vpc" "default_vpc"{
  default = true
}

data "aws_subnet_ids" "default_subnet" {
  vpc_id = data.aws_vpc.default.vpc_id
}

Providers

• Implement resource types and expose APIs.
• Define provider source (e.g., hashicorp/google) and arguments like project and region.

provider "google" {
  project = "my-project-id"
  region  = "us-central1"
  version = ">= 4.0"
}

Variables

• Allow flexible configurations without modifying source code.

1. Defines Variables

variable.tf

# String
variable "bucket_name" {
  description = "Name of the S3 bucket"
  type        = string
}
# List
variable "instance_types" {
  type    = list(string)
  default = ["t2.micro", "t3.micro"]
}
# Map
variable "storage_type" {
  type = map(string)
  default = {
    standard = "gp2"
    high     = "io1"
  }
}
# Set
variable "team_members" {
  type    = set(string)
  default = ["alice", "bob", "charlie", "dave"]
}

2. Using Variables

# Use string
resource "aws_s3_bucket" "example" {
  bucket = var.bucket_name
}
# Use list with count
resource "aws_instance" "example1"{
  count = length(var.instance_types)
  instance_type = var.instance_types[count.index]
}
# Use map var with for_each 
resource "aws_instance" "example2" {
  for_each      = var.storage_type
  ami           = "ami-12345678"
  instance_type = each.value
  tags = {
    Name = each.key
  }
}
# Use set var with for_each 
resource "aws_iam_user" "team" {
  for_each = var.team_members
  name     = each.value
}

You can also pass variable at runtime

terraform apply -var="VAR_NAME=VALUE" -var="VAR_NAME=VALUE"

Best Practices:

• Parameterize selectively
• Use .tfvars for root modules
• Name descriptively
• Prefer positive boolean names
• Always add descriptions

Outputs

• Expose resource attributes for reference.

output "bucket_url" {
  value = google_storage_bucket.example.self_link
}

Backend (State Management Storage)

• Stores resource terraform.tfstate locally (default)
• Stores remotely AWS S3, GCP GCS, Azure Blob, Terraform Cloud, or GitLab.
• Enables team collaboration and locking mechanisms

1. GCP Remote Backend

terraform {
  backend "gcs" {
    bucket = "my-bucket"
    prefix = "terraform/state"
  }
}

2. AWS Remote Backend

terraform {
  backend "s3" {
    bucket = "my-bucket"
    key = "tf-infra/terraform.tfstate"
    region = "us-east-1"
    dynamodb_table = "terraform-state-locking"  # state locking to prevent concurrent modifications
    encrypt = true  
  }
}

3. Terraform Cloud Remote Backend

terraform {
  backend "remote" {
    hostname     = "app.terraform.io"
    organization = "my-org"

    workspaces {
      name = "my-workspace"
    }
  }
}

Best Practices:

• Use remote state for teams
• Encrypt state files
• Avoid storing secrets
• Don't manually modify state

Modules

• Reusable Terraform configurations, local or remote.

module "network" {
  source = "./modules/network"
}

Best Practices:

• Avoid excessive modularization
• Use count / for_each for repetition
• Parameterize meaningfully
• Organize with local modules
• Use Terraform Registry