Terraform: How to convert relative paths to absolute paths

Introduction

When working with Terraform, managing file paths efficiently can streamline your infrastructure provisioning process. Often, you’ll start with relative paths for simplicity and readability. However, as your project grows in complexity, the need for converting these relative paths to absolute paths becomes evident, ensuring consistency and eliminating errors due to path misunderstandings. In this tutorial, we’ll explore how to convert relative paths to absolute paths in Terraform, enhancing your infrastructure as code practices.

Understanding Paths in Terraform

Terraform manipulates paths in several contexts, like when specifying a module source or working with file-based functions. A relative path is defined in relation to the current working directory, whereas an absolute path, which begins from the root directory, provides a full path to a specific file or directory.

Basic Conversion: Using the abspath Function

One of Terraform’s built-in functions, abspath, is the simplest way to convert a relative path to an absolute path. Consider the following example:

locals {
  my_relative_path = "some/dir"
  my_absolute_path = abspath(local.my_relative_path)
}
output "absolute_path" {
  value = local.my_absolute_path
}

This will output the absolute path of `some/dir` relative to the current working directory.

Advanced Usage: Combining path.module with abspath

If you’re dealing with modules and need to convert paths within them, you can combine abspath with path.module for more precise control. path.module returns the filesystem path of the module where it’s called. Here’s how you can use these functions together:

locals {
  module_relative_path = "../../modules/mymodule"
  module_absolute_path = abspath(path.module, local.module_relative_path)
}
output "module_absolute_path" {
  value = local.module_absolute_path
}

Working with External Data and Scripts

When your Terraform configuration depends on external data or needs to execute scripts, absolute paths become crucial for reliability. You can dynamically create absolute paths for such purposes:

data "external" "example" {
  program = ["${abspath("./scripts/my_script.sh")}"]
}

This ensures that Terraform executes `my_script.sh` from an accurate location regardless of the current working directory.

Combining Paths

Sometimes, you might need to build a complex path by combining multiple segments. Terraform’s path.root function, together with string interpolation or the join function, allows for the construction of such paths. Here’s an example:

locals {
  combined_path = "${path.root}/data/${var.some_variable}/file.txt"
}
output "combined_path" {
  value = local.combined_path
}

This combines path.root, a variable, and a fixed string to construct a path dynamically.

Error Handling and Best Practices

When converting paths, it’s crucial to handle errors gracefully, especially if you’re dynamically constructing paths based on input variables. Consider validating paths before using them. Moreover, using absolute paths helps in documentation and troubleshooting, providing clear and unambiguous references to files and directories.

Conclusion

Converting relative paths to absolute paths in Terraform promotes more reliable and maintainable infrastructure as code practice. Whether you’re working on a simple project or a complex module-based architecture, leveraging the power of Terraform’s abspath and related functions ensures your paths are always correctly resolved. This straightforward practice can significantly reduce errors and improve the clarity of your configurations.