Provisioning Multiple AWS EC2 Instances Using Terraform: for_each vs count

Infrastructure as Code (IaC) is a core skill for any DevOps engineer, and Terraform is one of the most widely used tools for this purpose.
In this article, I’ll walk through two practical ways to create multiple EC2 instances in AWS using Terraform:

1. Using for_each for environment-based instances

2. Using count for creating identical instances

This blog is based on my hands-on Terraform real execution results

Why Multiple Instances with Terraform?

In real-world environments, we often need:

• Different EC2 instances for dev, qa, prod

• Or multiple identical instances for scaling or testing

Terraform provides two powerful meta-arguments to achieve this:

• for_each

• count

Let’s understand both with hands-on examples.

Approach 1: Creating Environment-Based EC2 Instances Using for_each

Objective

Create EC2 instances for different environments (dev, qa, prod) with different instance types using a single Terraform configuration.

Terraform Folder Structure

.
├── main.tf
├── variables.tf
├── outputs.tf

variables.tf

variable "env_instances" {
  description = "Map of environments and their instance types"
  type        = map(string)
  default = {
    dev  = "t2.micro"
    qa   = "t2.small"
    prod = "t2.medium"
  }
}
variable "ami_id" {
  description = "AMI ID to use for all instances"
  type        = string
  default     = "ami-0c02fb55956c7d316"
}
variable "region" {
  description = "AWS region"
  type        = string
  default     = "us-east-1"
}

Why map?
Each environment acts as a key, making resource management more readable and predictable.

main.tf

provider "aws" {
  region = var.region
}
resource "aws_instance" "env_instances" {
  for_each      = var.env_instances
  ami           = var.ami_id
  instance_type = each.value
  tags = {
    Name        = "${each.key}-instance"
    Environment = each.key
  }
}

Key Insight

• each.key → environment name (dev / qa / prod)

• each.value → instance type

outputs.tf

output "instance_ids" {
  value = { for k, v in aws_instance.env_instances : k => v.id }
}
output "instance_public_ips" {
  value = { for k, v in aws_instance.env_instances : k => v.public_ip }
}

Execution Steps

terraform init
terraform plan
terraform apply

After applying, Terraform creates three EC2 instances, each mapped to its environment.

Expected Output

| Environment | Instance Name | Instance Type |
| dev | dev-instance | t2.micro |
| qa | qa-instance | t2.small |
| prod | prod-instance | t2.medium |

AWS Console confirms all instances are running successfully

Approach 2: Creating Identical EC2 Instances Using count

Objective

Create multiple identical EC2 instances using Terraform count.

variables.tf

variable "instance_count" {
  description = "Number of identical EC2 instances"
  default     = 3
}
variable "instance_type" {
  default = "t2.micro"
}
variable "ami_id" {
  default = "ami-0f9708d1cd2cfee41"
}
variable "availability_zone" {
  default = "ap-south-1a"
}

main.tf

resource "aws_instance" "count_instances" {
  count             = var.instance_count
  ami               = var.ami_id
  instance_type     = var.instance_type
  availability_zone = var.availability_zone

  tags = {
    Name = "count-instance-${count.index + 1}"
  }
}

How count works

• count.index starts from 0

• Useful when resources are identical

outputs.tf

output "instance_ids" {
  value = [for i in aws_instance.count_instances : i.id]
}

output "instance_public_ips" {
  value = [for i in aws_instance.count_instances : i.public_ip]
}

Execution Steps

terraform init
terraform plan
terraform apply

Expected Output

| Instance Name | Instance Type | AZ |
| count-instance-1 | t2.micro | ap-south-1a |
| count-instance-2 | t2.micro | ap-south-1a |
| count-instance-3 | t2.micro | ap-south-1a |

Verified successfully in AWS EC2 Console

for_each vs count – When to Use What?

| Feature | for_each | count |
| Resource identity | Key-based | Index-based |
| Best for | Env-based, unique configs | Identical resources |
| Readability | High | Moderate |
| Deleting one item | Safe | Risky (index shift) |

Final Thoughts

Use for_each when:

• Environments differ (dev / qa / prod)

• You want safer, more readable infrastructure

Use count when:

• Resources are identical

• You only care about quantity

Both approaches are essential for real-world Terraform usage, and mastering them makes your IaC clean, scalable, and production-ready.