Last Updated on May 11, 2024 by Arnav Sharma

Terraform, a leading Infrastructure as Code (IaC) tool recommended by many on platforms like Medium, offers various meta-arguments to manage infrastructure components efficiently. One of these meta-arguments is the for_each loop, a powerful construct that allows you to deploy multiple similar resources without duplicating configuration files. In this blog, we’ll delve deep into the for_each meta-argument, its advantages, and practical examples.

Understanding the for_each Meta-Argument

The for_each meta-argument in Terraform is used to iterate over a data structure, such as a list or map, configuring resources or module blocks with each item in turn. This dynamic block is particularly useful when you have multiple similar resources, like virtual machines or Kubernetes pods, that share the same lifecycle but need different configurations. Terraform’s for_each is one of the looping constructs introduced in version 0.13, alongside the well-known count.

Basic Usage of for_each

Simple List Example:

Let’s take a list of Avengers as an input variable. Using for_each, we can iterate over this list to create multiple instances of a resource, e.g., virtual machines.

locals {
  avengers = ["ironman", "captain america", "thor"]
}

resource "azurerm_virtual_machine" "avengers_vm" {
  for_each = toset(local.avengers)
  vm_size  = "t2.nano"
  name    = each.value

  tags = {
    name = each.key
  }
}

Using for_each with Maps:

Maps naturally provide uniqueness with their keys. Using for_each with a map of objects allows for more detailed configurations. For instance, deploying multiple EC2 instances using different configurations:

locals {
  ec2_configs = {
    "Ironman" = { instance_type = "t2.nano", ami = "ami-xyz" },
    "Thor"    = { instance_type = "t2.micro", ami = "ami-abc" }
  }
}

resource "aws_ec2_instance" "heroes" {
  for_each      = local.ec2_configs
  instance_type = each.value.instance_type
  ami           = each.value.ami

  tags = {
    Name = each.key
  }
}

Advanced Usage with Dynamic Nested Blocks

Dynamic nested blocks in Terraform allow for building repeated nested configurations. For instance, when defining security group rules in Azure, we can use dynamic nested blocks to define multiple inbound security rules:

resource "azurerm_network_security_group" "example" {
  name                = "example-nsg"
  location            = azurerm_resource_group.example.location
  resource_group_name = azurerm_resource_group.example.name

  dynamic "security_rule" {
    for_each = local.rules
    content {
      name                        = security_rule.key
      priority                    = security_rule.value.priority
      direction                   = "Inbound"
      access                      = "Allow"
      protocol                    = "Tcp"
      source_port_range           = "*"
      destination_port_range      = security_rule.value.port
      source_address_prefix       = "*"
      destination_address_prefix  = "*"
    }
  }
}

Practical Azure Example with for_each

Using for_each, we can create multiple storage accounts in Azure. The following example demonstrates how to use for_each to create storage accounts with custom tags:

resource "azurerm_storage_account" "example" {
  name                     = "storageaccount${each.key}"
  resource_group_name      = azurerm_resource_group.example.name
  location                 = azurerm_resource_group.example.location
  account_tier             = "Standard"
  account_replication_type = "LRS"

  for_each = var.custom_tags

  tags = {
    environment = each.value
  }
}

count vs. for_each

While both count and for_each are used for looping in Terraform, they serve different purposes. The count method is often used when you want to create a fixed number of identical resources. On the other hand, for_each is more suitable when dealing with resources that need unique configurations.

It’s essential to note that count and for_each are mutually exclusive, meaning you cannot use them together for a single resource. However, there are workarounds to combine their functionalities.

The for_each loop in Terraform provides a powerful way to manage multiple resources efficiently. By understanding its usage and nuances, developers and infrastructure engineers can harness its full potential to write cleaner and more maintainable Terraform code.

FAQ – Terraform for_each Meta-argument

Q: What is Terraform?

A: Terraform is an open-source infrastructure as code software tool that allows you to define and provision your cloud infrastructure resources using a declarative configuration language. It is developed by HashiCorp.

Q: How does Terraform work?

A: Terraform works by using a declarative configuration language to define and describe the desired state of your infrastructure. It then creates an execution plan based on that description and applies the changes to your infrastructure resources to bring them to the desired state.

Q: What is a resource block in Terraform?

A: A resource block in Terraform is used to define and provision a specific resource in your cloud infrastructure. It specifies the resource type, provider, and configuration settings.

Q: What is the purpose of the meta-argument in Terraform?

A: A meta-argument in Terraform is a special argument that can be used to modify the behavior of a resource or module. It provides additional functionality or customization options.

Q: How can I deploy multiple AWS EC2 instances in Terraform?

A: To deploy multiple EC2 instances in Terraform, you can use the `count` or `for_each` meta-argument in your resource block. This allows you to define a set of strings or a map or a set of objects to create multiple similar resources.

Q: What is the difference between the `count` and `for_each` meta-arguments in Terraform?

A: The `count` meta-argument in Terraform is used to create a fixed number of resources based on the value provided. The `for_each` meta-argument, on the other hand, is used to create resources based on a map or set of values.

Q: Can I use Terraform to deploy resources in Kubernetes?

A: Yes, you can use Terraform to deploy resources in Kubernetes. Terraform has a Kubernetes provider that allows you to manage and provision Kubernetes resources, such as pods, services, deployments, and more.

Q: What is a module block in Terraform?

A: A module block in Terraform is used to define and configure reusable sets of resources. It allows you to encapsulate a group of related resources into a module and use it across different Terraform configurations.

Q: What is Terraform state?

A: Terraform state is a file that keeps track of the resources that Terraform manages. It stores information about the current state of your infrastructure and is used to plan and apply changes to your resources.

Q: How can I use Terraform modules?

A: To use Terraform modules, you define a module block in your Terraform configuration and specify the source of the module. This can be a local directory or a remote repository. You can then use the resources defined in the module within your configuration.

Q: What is Terraform Loop Tutorial?

A: Terraform Loop Tutorial is a tutorial that explains how to use loops in Terraform to manage infrastructure as code. It covers topics such as using the for_each and count meta-arguments, creating multiple resources using a loop, and dynamically configuring resources.

Q: How can loops be used in Terraform?

A: Loops can be used in Terraform to create multiple resources based on a set of input values. This allows for the definition of repetitive infrastructure objects in a concise and efficient manner.

Q: What is the difference between Terraform for_each and count?

A: The for_each meta-argument in Terraform is used to create multiple instances of a resource based on a set of strings or objects. The count meta-argument, on the other hand, is used to create a fixed number of instances of a resource.

Q: How can I use for_each in Terraform code?

A: To use for_each in Terraform, you can define a map or set of strings as a variable and then use it in the resource block. Terraform will create a separate instance of the resource for each element in the map or set.

Q: Can I use for_each with existing resources in Terraform?

A: No, for_each can only be used to create new resources in Terraform. If you want to manage existing resources, you should use count instead.

Q: What is the syntax for using for_each in Terraform?

A: The syntax for using for_each in Terraform is as follows:resource_type resource_name { for_each = { key1 = value1, key2 = value2, … } # Resource configuration goes here }

Q: What is terraform count?

A: Terraform count is a meta-argument that is used to create a fixed number of instances of a resource. It takes an integer value as input and creates the specified number of instances.

Q: Can I use count and for_each together in Terraform?

A: No, count and for_each cannot be used together in the same resource block in Terraform. You should choose either count or for_each, depending on your requirements.

Q: How can I configure resources using dynamic blocks in Terraform?

A: Dynamic blocks in Terraform allow you to create multiple configurations within a single resource block. You can use them to iterate over a nested data structure and dynamically configure resources based on its contents.

Q: What are some recommended resources for learning Terraform?

A: If you are looking for resources to learn Terraform, you can check out tutorials and articles on HashiCorp website. They provide comprehensive and beginner-friendly tutorials on various Terraform concepts and best practices.

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