Mastering Terraform’s for_each with Real-World Examples

Terraform’s for_each construct lets you dynamically create multiple instances of a resource, module, or block using a map or set of strings. This eliminates repetitive code, improves maintainability, and unlocks more powerful patterns in infrastructure as code.

In this guide, we’ll explore how for_each works in Terraform, when to use it over count, and show real-world examples for AWS resources like EC2 instances, S3 buckets, and security groups.

Why for_each Is Powerful

Terraform supports two ways to loop over resources: count and for_each. While count uses numeric indexes, for_each lets you iterate over:

• Maps (key-value pairs)
• Sets of strings (unique elements)

This allows you to name each resource instance logically and access attributes using meaningful keys instead of index numbers.

Basic Syntax

resource "aws_s3_bucket" "example" {
  for_each = toset(["logs", "archive", "media"])

  bucket = "${each.key}-bucket"
  acl    = "private"
}

This example creates three S3 buckets: logs-bucket, archive-bucket, and media-bucket.

for_each vs count

Example 1: Creating Multiple EC2 Instances

variable "instances" {
  default = {
    web01 = "t3.micro"
    web02 = "t3.small"
  }
}

resource "aws_instance" "web" {
  for_each = var.instances

  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = each.value
  tags = {
    Name = each.key
  }
}

This will create two EC2 instances with different sizes and logical names as tags.

Example 2: Looping Over a Set of Strings

locals {
  buckets = toset(["images", "logs", "backups"])
}

resource "aws_s3_bucket" "bucket" {
  for_each = local.buckets

  bucket = "${each.key}-project"
  acl    = "private"
}

each.key in this case is the bucket name string, since we’re looping over a set.

Example 3: Modules with for_each

You can use for_each to create multiple instances of a module:

module "vpc" {
  source = "./modules/vpc"

  for_each = {
    dev  = "10.0.0.0/16"
    prod = "172.16.0.0/16"
  }

  name       = each.key
  cidr_block = each.value
}

This creates two VPCs with different names and CIDR blocks.

Best Practices

• Use for_each when working with named collections (maps/sets)
• Keep keys stable to avoid resource recreation
• Use each.key and each.value clearly in nested structures
• For ordered collections, prefer count if numeric order matters

Final Thoughts

Terraform’s for_each construct is one of the most powerful tools in your infrastructure-as-code toolkit. It allows you to write declarative loops without sacrificing readability or control. By leveraging it properly, you can create reusable modules, simplify resource duplication, and build scalable environments across any cloud provider.

Whether you’re launching instances, provisioning S3 buckets, or templating modules — for_each is key to clean, DRY, and maintainable Terraform code.