Terraform count vs for_each: Which is Better for Dynamic Resources?

Terraform count vs for_each: Which is Better for Dynamic Resources?

When creating multiple instances of a resource in Terraform, you have two options: count and for_each. Knowing when to use each one is a key concept for writing reliable, maintainable infrastructure code.

Using count

count creates resources using a numeric index starting at 0. It is simple and works well for identical resources.

resource "aws_instance" "server" {
  count         = 3
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"

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

Resources are referenced as aws_instance.server[0], aws_instance.server[1], etc.

The Problem with count

If you remove an item from the middle of the list — say you delete index 1 — Terraform will shift all subsequent indices and recreate every resource after the deleted one. This is dangerous in production environments.

# Before: ["server-a", "server-b", "server-c"]
# After removing "server-b": ["server-a", "server-c"]
# Terraform will DESTROY server-c and RECREATE it as the new index 1!

Using for_each (Recommended)

for_each uses a map or set of strings as unique keys, so each resource is tied to a stable identifier — not a fragile numeric index.

variable "servers" {
  default = {
    "server-a" = "t2.micro"
    "server-b" = "t2.small"
    "server-c" = "t2.micro"
  }
}

resource "aws_instance" "server" {
  for_each      = var.servers
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = each.value

  tags = {
    Name = each.key
  }
}

Resources are referenced as aws_instance.server["server-a"]. Removing “server-b” only destroys that specific resource, leaving others untouched.

for_each with a Set of Strings

resource "aws_iam_user" "devs" {
  for_each = toset(["alice", "bob", "charlie"])
  name     = each.key
}

Quick Comparison

Key Takeaway

Prefer for_each over count for any resource list that may change over time. It provides stable, key-based identity and prevents unintended resource replacement when items are added or removed.