Day 15 – Creating Multiple Resources in Terraform with count and for_each

When working with Terraform, you’ll often need to create multiple resources — such as several subnets, EC2 instances, or even IAM users. Instead of copying and pasting the same resource block again and again, Terraform gives us two powerful features:

👉 count – create multiple identical (or almost identical) resources.
👉 for_each – create multiple resources from a map or set, with more control over naming and customization.

Let’s explore both with easy-to-follow examples.

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1. Using count

The count meta-argument allows you to create a specific number of resources.

Example: Creating 3 Subnets

resource "aws_subnet" "example" {
  count             = 3
  vpc_id            = aws_vpc.main.id
  cidr_block        = "10.0.${count.index}.0/24"
  availability_zone = element(["us-east-1a", "us-east-1b", "us-east-1c"], count.index)
}

✅ Here:

• count = 3 → Creates 3 subnets.

• count.index → Automatically gives us 0,1,2 for naming or CIDR assignment.

• Each subnet goes into a different AZ.

This is perfect when you just need a fixed number of similar resources.

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2. Using for_each

The for_each meta-argument allows you to create multiple resources based on a map or set of strings. This gives you names you control, instead of just numbers.

Example: Creating Subnets with Custom Names

variable "subnets" {
  default = {
    public  = "10.0.1.0/24"
    private = "10.0.2.0/24"
    db      = "10.0.3.0/24"
  }
}

resource "aws_subnet" "example" {
  for_each          = var.subnets
  vpc_id            = aws_vpc.main.id
  cidr_block        = each.value
  availability_zone = "us-east-1a"
  tags = {
    Name = "${each.key}-subnet"
  }
}

✅ Here:

• for_each loops over the map of subnets.

• each.key gives the subnet type (public, private, db).

• each.value gives the subnet CIDR.

This is more flexible than count when your resources aren’t identical.

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3. Multiple EC2 Instances with count

Example: Launch 3 identical EC2 Instances

resource "aws_instance" "web" {
  count         = 3
  ami           = "ami-12345678"
  instance_type = "t2.micro"

  tags = {
    Name = "web-${count.index}"
  }
}

✅ Terraform creates web-0, web-1, web-2.
Great when all instances are the same.

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4. Multiple EC2 Instances with Different AMIs (using for_each)

Sometimes, you want different configurations per instance.

variable "instances" {
  default = {
    ubuntu = "ami-12345678"
    amazon = "ami-87654321"
    debian = "ami-56781234"
  }
}

resource "aws_instance" "servers" {
  for_each      = var.instances
  ami           = each.value
  instance_type = "t2.micro"

  tags = {
    Name = "${each.key}-server"
  }
}

✅ Terraform creates:

• ubuntu-server with its AMI.

• amazon-server with its AMI.

• debian-server with its AMI.

This is the cleanest way to manage different resources with custom settings.

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5. When to Use count vs for_each

• Use count when you want a specific number of similar resources.

• Use for_each when you have unique names or values to assign to resources.

Think of it like this:

• count = "repeat this block N times".

• for_each = "loop over this map/set and create resources for each item".

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Conclusion

Terraform’s count and for_each meta-arguments make your code more reusable, cleaner, and dynamic.

• count is best for identical resources.

• for_each is best for resources with different values or names.

Once you master these, you’ll stop writing repetitive Terraform code and start writing scalable infrastructure.

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