How to Use for_each in Terraform: Syntax and Examples

In Terraform, for_each lets you create multiple resource instances from a map or set of strings by looping over each item. You define for_each inside a resource block, and Terraform creates one resource per item with unique keys.

Syntax

The for_each argument is used inside a resource or module block to create multiple instances based on a collection. It accepts a map or set of strings. Each instance gets a unique key from the collection.

Parts explained:

• resource: Defines the resource type and name.
• for_each: The collection to loop over (map or set).
• each.key: The current key in the loop.
• each.value: The current value in the loop.

terraform

resource "aws_instance" "example" {
  for_each = {
    server1 = "10.0.0.1"
    server2 = "10.0.0.2"
  }

  ami           = "ami-123456"
  instance_type = "t2.micro"
  private_ip    = each.value
  tags = {
    Name = each.key
  }
}

Example

This example creates two AWS EC2 instances with different private IPs and names using for_each. Terraform will create one instance per map entry.

terraform

provider "aws" {
  region = "us-east-1"
}

resource "aws_instance" "example" {
  for_each = {
    server1 = "10.0.1.10"
    server2 = "10.0.1.11"
  }

  ami           = "ami-0c55b159cbfafe1f0"  # Example AMI
  instance_type = "t2.micro"
  private_ip    = each.value

  tags = {
    Name = each.key
  }
}

Output

Apply complete! Resources: 2 added, 0 changed, 0 destroyed.

Common Pitfalls

Common mistakes when using for_each include:

• Using a list instead of a map or set of strings, which causes errors.
• Not using each.key or each.value properly inside the resource.
• Changing keys in the map between runs, which can cause resource replacement.

Always use stable keys in the map to avoid unexpected resource recreation.

terraform

/* Wrong: Using a list with for_each causes error */
resource "aws_instance" "wrong" {
  for_each = toset(["10.0.0.1", "10.0.0.2"])  # This is a set of strings, valid for for_each

  ami           = "ami-123456"
  instance_type = "t2.micro"
  private_ip    = each.value
}

/* Right: Use a map with keys */
resource "aws_instance" "right" {
  for_each = {
    server1 = "10.0.0.1"
    server2 = "10.0.0.2"
  }

  ami           = "ami-123456"
  instance_type = "t2.micro"
  private_ip    = each.value
}

Quick Reference

Term	Description
for_each	Loops over a map or set to create multiple resource instances.
each.key	The current key in the loop, used to identify the instance.
each.value	The current value in the loop, used for resource properties.
Map	A collection of key-value pairs, recommended for stable keys.
Set of strings	A collection of unique strings, can also be used with for_each.

Key Takeaways

Use for_each with maps or sets of strings to create multiple resource instances.

Always reference each.key and each.value inside the resource block for dynamic values.

Avoid using lists directly with for_each to prevent errors.

Keep keys stable between runs to avoid resource replacement.

for_each helps write cleaner, reusable Terraform code for multiple similar resources.