Last Updated on September 19, 2024 by Arnav Sharma
Terraform has revolutionized the way DevOps engineers and data scientists manage and provision infrastructure. With its unique Hashicorp Code Language (HCL), Terraform offers a robust coding structure, making it a popular infrastructure tool. Among its myriad features, Terraform Local Values, often termed as “locals,” stand out as a pivotal component. This Saturn Cloud blog aims to provide an in-depth understanding of Terraform Local Values, their declaration, usage, best practices, and practical examples with Azure.
What Exactly is a Terraform Local Value?
In the vast sea of Terraform configurations, a local value is like a beacon. It assigns a name to an expression, allowing users to reference the name multiple times within a module. This eliminates the need to repeat the expression, making the Terraform code more concise and readable. Drawing a parallel with traditional programming languages, Terraform modules can be likened to function definitions:
- Input variables equate to function arguments.
- Output values are analogous to function return values.
- Local values can be compared to a function’s temporary local variables.
For simplicity, local values are often termed as “locals” when the context makes the meaning evident.
Azure-Specific Examples with Terraform Locals
Azure Virtual Network Name Composition: Suppose you have a naming convention for your Azure Virtual Networks that combines the environment, region, and a static string.
locals {
env = "prod"
region = "westus"
vnet_name = "${local.env}-${local.region}-vnet"
}
Using the local value in an Azure Virtual Network resource:
resource "azurerm_virtual_network" "example" {
name = local.vnet_name
address_space = ["10.0.0.0/16"]
location = azurerm_resource_group.example.location
resource_group_name = azurerm_resource_group.example.name
}
Azure Resource Group Naming: Creating a local value for Azure Resource Group name:
locals {
rg_name = "tf-rg-${local.env}"
}
Using the local value in an Azure Resource Group:
resource "azurerm_resource_group" "example" {
name = local.rg_name
location = "West US"
}
Azure Storage Account Name Composition: Azure storage account names need to be unique across Azure and can only contain lowercase letters and numbers. Using locals can help generate such names.
locals {
sa_prefix = "tfstg"
sa_suffix = "001"
sa_name = "${local.sa_prefix}${local.sa_suffix}"
}
Using the local value in an Azure Storage Account:
resource "azurerm_storage_account" "example" {
name = local.sa_name
resource_group_name = azurerm_resource_group.example.name
location = azurerm_resource_group.example.location
account_tier = "Standard"
account_replication_type = "LRS"
}
Key Takeaways and Best Practices
Terraform locals are a powerful tool for simplifying Terraform configurations. They enhance code readability and reduce repetition. With the added Azure-specific examples, you can now see how locals can be effectively used in real-world scenarios, making your Terraform configurations more modular and maintainable. As you continue your journey with Terraform, remember to use locals judiciously. Combine them effectively with other Terraform components for optimal results, and always keep an eye on the Terraform state to ensure consistency.
Harnessing the Power of Terraform Locals
The use of local values can be helpful to avoid repeating the same values and expressions multiple times within a Terraform configuration. While they are a powerful tool, if overused, they can also make a configuration hard to read by future maintainers by hiding the actual values used. Therefore, it’s essential to strike a balance. As you delve deeper into the world of IaC and Terraform, locals will undoubtedly become one of your go-to tools to streamline and optimize your configurations.
FAQ – Terraform Variable
Q: What is the purpose of using a local block in Terraform?
A: The local block is used to define local variables within a Terraform configuration. This allows you to assign a name to the result of any Terraform expression and reuse that name throughout your configuration. A key advantage of local values is the ability to easily change the value in one place, especially when the value is used multiple times within the configuration or module.
Q: How do Terraform input variables differ from local variables?
A: Terraform input variables are used to pass dynamic values during or between Terraform runs, such as during a plan or apply. They allow you to input values from outside the configuration, making your configurations more flexible and reusable. In contrast, local variables are used to define values that are used multiple times within a configuration. Unlike input variables, locals are not set directly by the user but are instead assigned within the configuration file.
Q: When should you use local values instead of input variables in Terraform?
A: You should use local values when you need to reuse a value or expression multiple times within a Terraform configuration or module. Locals are ideal for defining values that are calculated or derived from input variables or other sources, making them easier to manage. Input variables, on the other hand, are better suited for values that need to be provided by the user or changed between different environments.
Q: What are some common use cases for using local variables in Terraform?
A: Common use cases for local variables in Terraform include:
- Assigning a name to a complex expression that is used multiple times in a configuration.
- Simplifying the reuse of resource attributes or other values across multiple resources or modules.
- Defining related local values that need to be consistent across the configuration.
- Allowing for easy changes to key values without modifying multiple parts of the configuration.
Q: How does using a local value help in managing Terraform configurations?
A: Using a local value helps in managing Terraform configurations by allowing you to assign a name to the result of any Terraform expression. This makes it easier to re-use that name throughout your configuration, reducing redundancy and the risk of errors. Additionally, locals can also be used to assign dynamic values that change based on other variables or conditions, making your configuration more flexible and maintainable.
Q: What is the relationship between locals and environment variables in Terraform?
A: Environment variables in Terraform are typically used to set input variables or other configuration settings at runtime, whereas locals are used within the Terraform configuration files themselves to define and reuse values. While both can influence the behavior of a Terraform run, locals are more focused on managing values within the configuration, whereas environment variables are more about controlling the Terraform process externally.
Q: Can you explain the difference between locals and variables inside a child module in Terraform?
A: In a child module, input variables are used to pass values from the parent module to the child module. Locals, on the other hand, are defined within the module itself and are used to manage values that are used multiple times within that specific module. The locals block is used to define these local variables, which can simplify the configuration and make it easier to change values used in many places within the module.