Terraform cloud failing when referencing module using relative local path

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06-10-2024

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Terraform Cloud: Overcoming the "Relative Path" Hurdle When Using Modules

Terraform modules are a powerful tool for organizing and reusing infrastructure code. However, when working with Terraform Cloud, you might encounter a frustrating error when referencing a module using a relative local path. This article explores this issue, provides a solution, and guides you on how to effectively manage modules within Terraform Cloud.

The Problem:

You've defined a Terraform module within your project and are attempting to reference it from another file using a relative path (e.g., ./modules/my-module). Terraform Cloud throws an error, indicating it cannot find the module at the specified location.

Example Scenario:

main.tf:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.0"
    }
  }
}

module "my_module" {
  source = "./modules/my-module"
  # ... other module variables ...
}

modules/my-module/variables.tf:

variable "instance_type" {
  type = string
  default = "t2.micro"
}

The Error:

Error: Failed to load module at "./modules/my-module":
  Error: Could not locate source: ./modules/my-module

Understanding the Issue:

The root of this problem lies in Terraform Cloud's execution environment. When you run terraform init on your local machine, Terraform searches for the module relative to the current working directory. However, Terraform Cloud executes your code in a separate, isolated environment where relative paths are not directly applicable.

The Solution: Using Module Registries

To overcome this limitation, Terraform Cloud encourages using module registries. These registries act as central repositories for storing and sharing Terraform modules.

Here's how to address the issue:

1. Choose a Module Registry: Popular options include:

   • Terraform Registry: The official registry maintained by HashiCorp.
   • Private Registries: Options like GitHub, GitLab, and private registries hosted on your infrastructure.

2. Publish Your Module: Follow the instructions provided by your chosen registry to upload and publish your module.

3. Reference the Module in Terraform Cloud:

   module "my_module" {
     source = "your-registry-name/your-module-name"
     # ... other module variables ...
   }
   

Example Using Terraform Registry:

Assuming you've published your module to the Terraform Registry as hashicorp/my-module, the main.tf file would be modified as follows:

module "my_module" {
  source = "hashicorp/my-module"
  # ... other module variables ...
}

Benefits of Module Registries:

• Centralized Management: Modules are stored and shared from a single source, promoting consistency and easier maintenance.
• Version Control: Registries allow you to track module versions, ensuring that your codebase relies on known and tested components.
• Collaboration: Teams can contribute to and leverage shared modules, improving efficiency and reusability.
• Security: Registries can be configured to enforce authentication and authorization, controlling module access.

Additional Considerations:

• Module Dependency Management: When using multiple modules, consider tools like terraform providers to manage their dependencies and ensure compatibility.
• Terraform Workspace: If you're working with multiple environments (e.g., development, staging, production), utilize Terraform workspaces to isolate your infrastructure configurations and avoid conflicts.
• Documentation: Document your modules thoroughly, including their purpose, input variables, and outputs, to ensure others can understand and utilize them effectively.

Conclusion:

While using relative paths for modules within your local environment might seem convenient, Terraform Cloud requires leveraging module registries for a more robust and scalable approach. By publishing your modules to a registry and referencing them accordingly, you can ensure your code executes smoothly on Terraform Cloud and enjoy the benefits of centralized module management.