Setting variable values in Terraform is a fundamental concept that allows you to create flexible and reusable infrastructure configurations. Variables enable you to parameterize your Terraform code, making it adaptable across different environments and use cases.
There are several methods to set v…Setting variable values in Terraform is a fundamental concept that allows you to create flexible and reusable infrastructure configurations. Variables enable you to parameterize your Terraform code, making it adaptable across different environments and use cases.
There are several methods to set variable values in Terraform, listed in order of precedence from lowest to highest:
1. **Default Values**: Define default values within variable blocks in your configuration files. If no other value is provided, Terraform uses these defaults.
2. **Environment Variables**: Set values using environment variables prefixed with TF_VAR_. For example, TF_VAR_region=us-west-2 sets the region variable.
3. **terraform.tfvars File**: Create a file named terraform.tfvars in your working directory. Terraform automatically loads this file and applies the variable values defined within it.
4. ***.auto.tfvars Files**: Any file ending with .auto.tfvars is automatically loaded by Terraform, allowing you to organize variables across multiple files.
5. **-var-file Flag**: Specify custom variable files using the -var-file flag during terraform plan or terraform apply commands. This allows loading different configurations for various environments.
6. **-var Flag**: Pass individual variable values through the command line using -var="variable_name=value". This method takes high precedence.
7. **Interactive Input**: If a required variable has no value set through any method, Terraform prompts for input during execution.
Variable types include string, number, bool, list, map, and object, providing flexibility in data representation. You can also mark variables as sensitive to prevent their values from appearing in logs or console output.
Best practices include using descriptive variable names, providing meaningful descriptions, setting appropriate default values for optional variables, and organizing variables logically. Understanding variable precedence is crucial for managing configurations across development, staging, and production environments effectively.
Setting Variable Values in Terraform
Why Setting Variable Values is Important
Variables are fundamental to creating flexible, reusable, and maintainable Terraform configurations. Understanding how to set variable values allows you to customize deployments across different environments (development, staging, production) using the same codebase. This is a core concept tested on the Terraform Associate exam.
What Are Variable Values?
In Terraform, input variables act as parameters for your modules and configurations. They allow you to pass different values into your Terraform code at runtime, making your infrastructure code dynamic and adaptable.
How to Set Variable Values - Methods and Precedence
Terraform provides multiple ways to set variable values, listed here from lowest to highest precedence:
1. Default Values Defined within the variable block in your configuration: variable "instance_type" { default = "t2.micro"}
2. Environment Variables Set using the TF_VAR_ prefix: export TF_VAR_instance_type="t2.small"
3. terraform.tfvars File Automatically loaded if present in the working directory: instance_type = "t2.medium"
4. *.auto.tfvars Files Any file ending in .auto.tfvars is automatically loaded in alphabetical order.
5. -var-file Flag Explicitly specify a variable file: terraform apply -var-file="prod.tfvars"
6. -var Flag (Command Line) Pass variables at the command line: terraform apply -var="instance_type=t2.large"
7. Interactive Prompt If no value is provided and no default exists, Terraform prompts for input during execution.
Variable Precedence Order (Most Important for Exam)
When the same variable is set in multiple places, Terraform uses this precedence (highest wins): -var and -var-file (last one wins) > *.auto.tfvars (alphabetical) > terraform.tfvars > Environment variables > Default values
Exam Tips: Answering Questions on Setting Variable Values
• Memorize the precedence order - This is frequently tested. Remember that command-line flags (-var) have the highest precedence.
• Know the automatic loading behavior - terraform.tfvars and *.auto.tfvars files are loaded automatically; other .tfvars files require the -var-file flag.
• Remember the environment variable prefix - Variables must use TF_VAR_ prefix (e.g., TF_VAR_region, not TERRAFORM_region).
• Understand that -var can be used multiple times - You can specify multiple variables: terraform apply -var="a=1" -var="b=2"
• Watch for trick questions - Questions may ask which value Terraform uses when a variable is set in multiple places. Always apply the precedence rules.
• Know that sensitive variables still need values - The sensitive argument only affects output display, not how values are set.
• Practice identifying file types - Know the difference between terraform.tfvars (auto-loaded), custom.tfvars (needs -var-file), and *.auto.tfvars (auto-loaded alphabetically).
Common Exam Question Patterns
Questions often present scenarios where a variable is defined in multiple locations and ask which value Terraform will use. Apply the precedence order to determine the correct answer. Also expect questions about the correct syntax for environment variables and command-line flags.