Terraform variables are an important feature of the Terraform Infrastructure-as-Code (IaC) management tool that enables the defining of values that can be passed into configurations. They are vital in creating dynamic and recyclable infrastructure code, which is one of the supposed benefits of shifting to IaC.
Variables are not unique to Terraform, though. Other IaC tools also have them or something similar. However, what makes Terraform variables different is the way they are designed for a declarative approach in making configurations, infrastructure abstraction, interpolation, and dynamic typing. Terraform users can take advantage of different types of variables to have flexibility in setting values for infrastructure configurations.
Types of Terraform Variables
There are at least six Terraform variable types, the first and most basic variable type being “string.” It is used for texts, Unicode characters to be specific. Strings can represent server names, resource names, API keys, file paths, URLs, tags, and message templates, among others.
Another variable is “number,” which obviously refers to numerical characters including zero, negative numbers, and decimals. These variables represent numbers of certain elements like the number of virtual machines, sizes of certain parameters, and other components that entail counts.
On the other hand, Terraform also has “bool” values, which indicate true or false conditions. These are used when setting toggles or switches in configurations. Bool is an abridged term for “Boolean.”
Additionally, Terraform has “list” variables that can contain similar types of values. For example, a list can show an array of IP addresses, URLs, server names, user names, or passwords.
Terraform also features the “map” variables. These are key-value pairs, which make it possible to associate values with specific keys. The map variable is also known as “object.” It can present a group of values with their respective labels like associating user IDs with user names.
“Object” variables may also be used to define a structure with multiple fields consisting of different variable types, which enables the creation of a custom data type to match specific requirements.
Maximizing the use of Variables
The variables listed above can be used ingeniously to achieve different possibilities and make IaC configuration and management flexible and reusable. Here are examples of key ways to make the most out of the different types of variables in Terraform.
Dynamic resource naming
Terraform supports the creation of resource names based on different parameters like project name, environment, and values that are tied to specific contexts. This enables dynamic resource naming, which simplifies the standardization of naming conventions across different resources and environments. It also makes it easy to perform resource identification.
Example:
variable “environment” {
type = string
default = “dev”
}
variable “project_x” {
type = string
default = “myproject”
}
resource “aws_instance” “example” {
ami = “ami-88888888”
instance_type = “t2.micro”
# Constructing the resource name dynamically
tags = {
Name = “${var.project_name}-${var.environment}-instance”
}
}
The code above demonstrates the defining of two variables (environment and project_x) to enable customization. There is a resource block (aws_instance) that employs the tags argument to enforce a tag for the instance. The value of this tag is dynamically generated through a string interpolation (${}), which points to the variable values.
Once applied, the configuration code above causes the generation of an AWS EC2 instance that has a dynamically created name derived from the environment and project_x variables. With the defaults indicated, the resulting instance name will be “myproject-dev-instance.” If values are entered (superseding the default), a new name is created following the same format.
Conditional settings
Variables are important in leveraging conditional logic to activate or deactivate features based on certain conditions or environmental environments. Conditional settings in Terraform make infrastructure code dynamic or adaptable to a variety of purposes or use cases without the need to redo the code or come up with separate configurations. They enhance code flexibility and significantly reduce maintenance.
Example:
variable “enable_instance” {
type = bool
default = true
}
resource “aws_instance” “example” {
ami = “ami-88888888”
instance_type = “t2.micro”
count = var.enable_instance ? 1 : 0
}
In the example above, a bool variable (enable_instance) is used with the default value of “true.” It has an aws_instance resource block that employs the count parameter and a conditional expression that relies on a number variable (1 or 0). If there is no input for the enable_instance variable, the default “true” value is recognized, which results in the creation of one instance. Otherwise, no instance is created.
Parameterized module instances
The parameterization of module instances makes Terraform modules reusable with various configurations for different sections of the infrastructure. It is done by passing variables to the module block, enabling module reuse through input variable customization.
The basic code for this is as follows:
module “web_server” {
source = “./modules/web”
instance_type = “t2.micro”
}
module “db_server” {
source = “./modules/db”
instance_type = “t3.small”
}
This code has two modules, namely “web_server” and “db_server.” These two represent different parts of the infrastructure. The module parameters can be strings, bool, numbers, maps, lists, or objects. In this case, the instance_type variables can be customized for the respective module instances, allowing the reuse of the two modules for other configurations according to unique requirements. This makes it possible for modular components to readily contain configurations and related resources for easy code reuse and maintenance.
Provider-specific information abstraction
Terraform variables support the abstraction of provider-specific details such as region, secret_key, access_key, and others. This function makes it possible to migrate to different cloud providers easily since the settings can be conveniently adjusted as needed. The variable types usually used for abstraction are string and numbers. Lists and maps may also be used.
The code looks like this:
provider “aws” {
region = var.aws_region
access_key = var.aws_access_key
secret_key = var.aws_secret_key
}
It is also possible to create a module for resources. The module acquires the provider-specific details as input variables, similar to what is shown below.
variable “instance_type” {
type = string
default = “t2.micro”
}
resource “aws_instance” “web_server” {
ami = “ami-88888888”
instance_type = var.instance_type
# Additional configuration for the web server…
}
More modules can be created to encapsulate different infrastructure requirement details. By doing this, switching between providers or environments does not have to be tedious and prone to errors. More importantly, the IaC code becomes more versatile and capable of easily coping with environment or platform changes. It also enables the sharing of the working code to those who have different provider configurations but are looking for better configurations.
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In summary
Terraform variable types have a pivotal role in the adaptability and flexibility of IaC code. They provide the means to easily scale up configurations and reuse infrastructure code for a different environment. Different Terraform variable types enable dynamic configurations that can evolve with the changes and growing needs of modern infrastructure. It is important for organizations that are mulling over the use of Terraform to be thoroughly acquainted with the uses of the different variables, especially when managing large infrastructure configurations.
