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Terraform

Terraform: Load Input Data from File (Examples)

By Filip on 10/07/2024

Learn how to efficiently load input data from external files into your Terraform configurations for more organized and manageable infrastructure as code.

Terraform: Load Input Data from File (Examples)

Table of Contents

Introduction

To load data from a file in Terraform, use the file() function. This function reads the content of a file on your local disk and returns it as a string. The file must exist at the beginning of the Terraform run.

Step-by-Step Guide

To load data from a file in Terraform, you can use the file() function. This function reads the content of a file on your local disk and returns it as a string.

Important: The file must exist at the beginning of the Terraform run, as functions are evaluated before any resources are created.

Here's how to use the file() function:

  1. Create a file: First, create a file with the data you want to load. For example, you could create a file named variables.txt with the following content:

    variable1 = "value1"
variable2 = "value2"

  2. Use the file() function: In your Terraform configuration file, use the file() function to read the content of the file you created. For example:

    locals {
  variables = file("variables.txt")
}

    This code reads the content of the variables.txt file and assigns it to a local variable named variables.

  3. Access the data: You can then access the data from the file by referencing the local variable. For example, to print the value of variable1, you could use the following code:

    output "variable1" {
  value = local.variables
}

Note: The file() function returns the entire content of the file as a single string. If you need to parse the data into a different format, you can use other Terraform functions like json_decode() or yamldecode().

For example, if your file data.json contains JSON data:

{
  "name": "example",
  "value": "123"
}

You can load and parse it like this:

locals {
  data = jsondecode(file("data.json"))
}

output "example_name" {
  value = local.data.name
}

This way, you can load data from files and use it to configure your infrastructure with Terraform.

Code Example

This code demonstrates two examples of loading data from files in Terraform. The first example reads the entire content of a text file as a string. The second example reads JSON data from a file, parses it, and then accesses specific attributes. These examples illustrate how to use the file() function and data parsing techniques to load and utilize data from files in Terraform configurations.

variables.txt:

variable1 = "value1"
variable2 = "value2"

main.tf:

locals {
  variables = file("variables.txt")
}

output "variable1" {
  value = local.variables
}

This example reads the content of variables.txt and outputs the entire content as a string.

Example 2: Loading and parsing JSON data

data.json:

{
  "name": "example",
  "value": "123"
}

main.tf:

locals {
  data = jsondecode(file("data.json"))
}

output "example_name" {
  value = local.data.name
}

output "example_value" {
  value = local.data.value
}

This example reads the JSON data from data.json, parses it using jsondecode(), and then accesses specific attributes like name and value.

These are just basic examples. You can adapt the file() function and data parsing techniques to load and utilize data from various file formats in your Terraform configurations.

Additional Notes

  • Security: Be cautious when storing sensitive data in files read by file(). Consider using Terraform's secure secret storage for such information.
  • Dynamic File Paths: You can use Terraform variables and functions to construct dynamic file paths for file(). This is useful for loading different files based on environments or conditions.
  • Templating: The content loaded by file() can be a template itself. You can use Terraform's built-in template language or external tools to generate dynamic content.
  • Alternatives: For more complex scenarios, consider using data sources like http to fetch data from remote sources or modules to encapsulate and reuse data loading logic.
  • Error Handling: If the specified file doesn't exist, Terraform will throw an error. You can use the try() function to handle potential errors gracefully.
  • Best Practices: Use descriptive file names and organize your data files logically to improve readability and maintainability.

Summary

This summary explains how to use the file() function in Terraform to load data from local files and utilize it in your configurations.

Key Points:

  • Purpose: The file() function reads the entire content of a local file and returns it as a string.
  • Requirement: The file must exist before the Terraform run starts.
  • Usage:
    1. Create a data file: This file can contain plain text, JSON, YAML, or any format you need.
    2. Read with file(): Use file("your_file.ext") within your Terraform code to read the file's content.
    3. Store and access: Assign the output of file() to a local variable for easy access and manipulation.
  • Data Parsing:
    • For structured data like JSON or YAML, use functions like jsondecode() or yamldecode() to parse the string returned by file() into usable data structures.
  • Example: 
    locals {
  variables = file("variables.txt") 
  data = jsondecode(file("data.json"))
}

Benefits:

  • Dynamic Configuration: Load variables, templates, or other data from external files to make your Terraform code more flexible and reusable.
  • Separation of Concerns: Keep sensitive or environment-specific data separate from your main configuration files.

Remember: The file() function reads the entire file as a single string. You are responsible for parsing and utilizing the data appropriately based on its format.

Conclusion

The file() function in Terraform is a powerful tool for loading data from your local files into your configurations. By reading file content as a string, you can dynamically define variables, load templates, and manage sensitive information separately. Remember to parse structured data appropriately using functions like jsondecode() or yamldecode(). By combining file() with other Terraform features, you can create more flexible, maintainable, and secure infrastructure deployments.

References

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