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For Loops

When you need to create multiple similar resources (like several subnets or IAM users), you could copy‑paste, but that’s error‑prone. Terraform provides count and for_each to iterate over lists and maps.

Using count

The count meta‑argument creates a number of instances of a resource. You can access the index with count.index.
variable "subnet_cidrs" {
  type    = list(string)
  default = ["10.0.1.0/24", "10.0.2.0/24", "10.0.3.0/24"]
}

resource "aws_subnet" "main" {
  count      = length(var.subnet_cidrs)
  cidr_block = var.subnet_cidrs[count.index]
  vpc_id     = aws_vpc.main.id
}

Using for_each

for_each works with a map or set of strings. It creates one resource per item, and you can access the key and value with each.key and each.value. It’s more flexible than count when you need to delete specific items.
variable "subnets" {
  type = map(object({
    cidr = string
    az   = string
  }))
  default = {
    "subnet1" = { cidr = "10.0.1.0/24", az = "us-east-1a" }
    "subnet2" = { cidr = "10.0.2.0/24", az = "us-east-1b" }
  }
}

resource "aws_subnet" "main" {
  for_each          = var.subnets
  cidr_block        = each.value.cidr
  availability_zone = each.value.az
  vpc_id            = aws_vpc.main.id
  tags = { Name = each.key }
}

for Expressions in Locals

You can transform lists or maps using for expressions.
locals {
  instance_names = [for i in range(3) : "web-${i}"]
  # result: ["web-0", "web-1", "web-2"]

  subnet_map = { for idx, cidr in var.subnet_cidrs : idx => cidr }
}

When to Use Count vs For_Each

  • count: When you need a simple list of identical resources and order matters.
  • for_each: When resources have distinct identifiers (like subnet names) and you may need to remove individual items without affecting others.


Two Minute Drill
  • count creates N copies; access with count.index.
  • for_each iterates over maps/sets; access with each.key and each.value.
  • Use for expressions to transform collections in locals.
  • Prefer for_each when resource identity matters for updates.

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