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Aisalkyn Aidarova
Aisalkyn Aidarova

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Terraform Lab: Count, Variables, Conditional Expressions

#aws #devops #terraform #tutorial

Lab Goal

  1. Terraform variable data types
  2. How to use count
  3. How to use count.index
  4. How to use conditional expressions
  5. How to deploy different infrastructure using dev.tfvars and prod.tfvars

Architecture

DEV
→ 1 EC2 instance

PROD
→ 3 EC2 instances

Step 1 — Create Project Folder 

mkdir terraform-count-lab
cd terraform-count-lab
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Create files:

main.tf
variables.tf
outputs.tf
dev.tfvars
prod.tfvars
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Step 2 — variables.tf (Data Types)

This file defines variable types.

variable "aws_region" {
  description = "AWS region"
  type        = string
}

variable "environment" {
  description = "Environment name"
  type        = string
}

variable "instance_type" {
  description = "EC2 instance type"
  type        = string
}

variable "instance_count" {
  description = "Number of instances"
  type        = number
}

variable "instance_names" {
  description = "List of instance names"
  type        = list(string)
}
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Important data types should know:

Type Example
string "t2.micro"
number 3
bool true
list ["web1","web2"]
map {env="dev"}

Step 3 — main.tf

This file creates EC2 instances using count.

provider "aws" {
  region = var.aws_region
}

data "aws_ami" "amazon_linux" {
  most_recent = true

  owners = ["amazon"]

  filter {
    name   = "name"
    values = ["amzn2-ami-hvm-*-x86_64-gp2"]
  }
}

resource "aws_instance" "web" {

  count = var.instance_count

  ami           = data.aws_ami.amazon_linux.id
  instance_type = var.instance_type

  tags = {
    Name = "${var.environment}-server-${count.index}"
  }
}
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Step 4 — Understanding count 

count = var.instance_count
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If

instance_count = 3
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Terraform creates

web[0]
web[1]
web[2]
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Step 5 — Understanding count.index 

Name = "${var.environment}-server-${count.index}"
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Example output:

DEV

dev-server-0
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PROD

prod-server-0
prod-server-1
prod-server-2
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Step 6 — Conditional Expression

Add this in main.tf.

Example:

instance_type = var.environment == "prod" ? "t2.small" : "t2.micro"
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Meaning:

If environment is prod

t2.small
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Else

t2.micro
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This is called Terraform ternary conditional.

Structure:

condition ? true_value : false_value
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Example:

var.environment == "prod" ? 3 : 1
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Step 7 — dev.tfvars 

aws_region = "us-east-2"

environment = "dev"

instance_type = "t2.micro"

instance_count = 1

instance_names = ["dev-server"]
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Step 8 — prod.tfvars 

aws_region = "us-east-2"

environment = "prod"

instance_type = "t2.small"

instance_count = 3

instance_names = ["prod-server1","prod-server2","prod-server3"]
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Step 9 — outputs.tf 

output "instance_ids" {
  value = aws_instance.web[*].id
}

output "instance_public_ip" {
  value = aws_instance.web[*].public_ip
}
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Step 10 — Initialize Terraform 

terraform init
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Step 11 — Deploy DEV 

terraform plan -var-file="dev.tfvars"
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terraform apply -var-file="dev.tfvars"
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Result:

1 EC2 instance
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Step 12 — Deploy PROD 

terraform plan -var-file="prod.tfvars"
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terraform apply -var-file="prod.tfvars"
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Result:

3 EC2 instances
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Step 13 — Destroy

DEV

terraform destroy -var-file="dev.tfvars"
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PROD

terraform destroy -var-file="prod.tfvars"
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