freundcloud

Terraform for_each, count, and for Expressions

Terraform provides several ways to create multiple resources dynamically, which is essential for scalable, cloud-agnostic DevOps workflows across AWS, Azure, and GCP. The most common patterns are count, for_each, and for expressions. Below are real-life, production-ready examples and best practices.

Using count (Index-Based Iteration)

Use count to create resources from a list, referencing each item by its index. This is simple but less flexible for complex objects or maps.

variable "storage_account_names" {
  type    = list(string)
  default = ["jackuksstr001", "jackuksstr002", "jackuksstr003"]
}

resource "azurerm_resource_group" "example" {
  name     = "storage-rg"
  location = "UK South"
}

resource "azurerm_storage_account" "my_storage" {
  count                    = length(var.storage_account_names)
  name                     = var.storage_account_names[count.index]
  resource_group_name      = azurerm_resource_group.example.name
  location                 = azurerm_resource_group.example.location
  account_tier             = "Standard"
  account_replication_type = "GRS"
}

Using for_each (Keyed Iteration)

Use for_each to iterate over a set, map, or list (converted to a set). This is preferred for named resources, as it allows referencing by key and is more robust for updates.

variable "storage_account_names" {
  type    = list(string)
  default = ["jackuksstr001", "jackuksstr002", "jackuksstr003"]
}

resource "azurerm_resource_group" "example" {
  name     = "storage-rg"
  location = "UK South"
}

resource "azurerm_storage_account" "my_storage" {
  for_each                 = toset(var.storage_account_names)
  name                     = each.value
  resource_group_name      = azurerm_resource_group.example.name
  location                 = azurerm_resource_group.example.location
  account_tier             = "Standard"
  account_replication_type = "GRS"
}

Using the for Expression (List/Map Comprehension)

Use for expressions to transform or filter lists/maps, or to output values from resources created with for_each or count.

resource "azurerm_storage_account" "my_storage" {
  for_each                 = toset(var.storage_account_names)
  name                     = each.value
  resource_group_name      = azurerm_resource_group.example.name
  location                 = azurerm_resource_group.example.location
  account_tier             = "Standard"
  account_replication_type = "GRS"
}

output "storage_account_ids" {
  value = [for name in var.storage_account_names : azurerm_storage_account.my_storage[name].id]
}

Filtering with for and if (Conditional Comprehension)

You can filter resources or outputs using an if clause in a for expression.

locals {
  grs_storage_accounts = [for sa in azurerm_storage_account.my_storage : sa if sa.account_replication_type == "GRS"]
}

output "grs_storage_account_names" {
  value = [for sa in local.grs_storage_accounts : sa.name]
}

Conditional Arguments in Resources

Use conditionals to set resource arguments dynamically (e.g., for multi-environment or multi-cloud deployments):

variable "environment" {
  default = "prod"
}

resource "azurerm_storage_account" "my_storage" {
  for_each                 = toset(var.storage_account_names)
  name                     = each.value
  resource_group_name      = azurerm_resource_group.example.name
  location                 = azurerm_resource_group.example.location
  account_tier             = "Standard"
  account_replication_type = var.environment == "prod" ? "GRS" : "LRS"
}

Best Practices

  • Use for_each for named resources and maps; use count for simple lists.
  • Use for expressions for output transformation and filtering.
  • Always use unique keys with for_each to avoid resource drift.
  • Prefer for_each for cloud resources that may be updated or deleted individually.
  • Use conditionals for multi-cloud, multi-environment, or feature-flagged deployments.

References

Tip: Use these patterns to keep your Terraform code DRY, scalable, and cloud-agnostic—especially in CI/CD and multi-cloud DevOps workflows.

Add to SUMMARY.md

- [Terraform for_each, count, and for Expressions](pages/terraform/tips/terraform-for_each.md)