Configure Juju Model Defaults With Terraform: A Feature Request

Hey everyone! Let's dive into a feature request that could make life a whole lot easier when managing Juju deployments with Terraform. We're talking about a native provider resource to set juju model-defaults. Currently, the workaround involves using the local-exec provisioner, which, let's be honest, isn't always the cleanest or most elegant solution. So, why the request, and what's the potential benefit?

The Core Problem: Configuring Juju Model Defaults

Okay, so what's the deal with juju model-defaults anyway? For those new to Juju, these are settings that apply to a specific model, essentially a working environment within your Juju controller. Think of it like setting up the parameters for how your applications will run: things like the cloud you're deploying to, the resource constraints, or any specific network configurations. These defaults are super important because they ensure consistency and control across your deployments. The challenge arises in automating this configuration, especially when you're using a tool like Terraform to provision your infrastructure.

Currently, the most common method to configure juju model-defaults involves using the local-exec provisioner. This allows you to run commands directly on the machine where Terraform is running, which in this case would be the machine that has access to the Juju controller. While this approach works, it comes with several drawbacks. Firstly, it ties your configuration to the machine where Terraform runs. If you move your Terraform setup, you have to ensure that all the dependencies and access rights are correctly configured. Secondly, it can make your Terraform configurations less readable and harder to maintain. You're essentially mixing infrastructure-as-code with ad-hoc command execution.

The core of the feature request is to have a dedicated resource within the Terraform Juju provider. This would abstract away the complexities of running commands directly and allow you to define your model defaults declaratively within your Terraform configuration. This means you could define your model defaults as part of your infrastructure code, version control it, and ensure consistent application across different environments. Having a dedicated resource would streamline the process, improve readability, and ultimately make managing Juju deployments with Terraform a more pleasant experience.

Why This Matters: Benefits of a Dedicated Resource

Creating a native provider resource for juju model-defaults would offer several significant advantages. Firstly, it drastically improves the readability and maintainability of your Terraform code. Instead of scattering local-exec provisioners throughout your configuration, you'd have a clean, dedicated resource that clearly defines your model defaults. This clarity is invaluable when collaborating with others or revisiting your code months later. The intent of the code is explicit, making it easier to understand and modify.

Secondly, a native resource enhances reusability. You could easily define a module that configures your model defaults and reuse it across multiple Juju models. This promotes standardization and reduces the chances of configuration drift. It ensures consistency in your deployment environments. You define it once, and use it everywhere.

Thirdly, it simplifies access control and security. Instead of relying on local-exec, the provider resource could manage access to the Juju controller using the same credentials and authentication mechanisms as other Juju resources. This centralizes and simplifies security management, reducing the risk of misconfigured access.

Fourthly, the resource allows for better error handling and reporting. The provider could provide more specific error messages and better feedback during the configuration process. This can significantly reduce the time spent troubleshooting issues.

In essence, a dedicated resource offers a more robust, manageable, and secure way to configure juju model-defaults within your Terraform workflows.

The Current Workaround: local-exec Provisioner

So, how do we get around this currently? As mentioned, the go-to method is using the local-exec provisioner in Terraform. This works, but it's not ideal. Let's take a closer look.

Here is a simple example:

resource "null_resource" "configure_model_defaults" {
  provisioner "local-exec" {
    command = "juju model-defaults ..."
    # Your Juju command with the necessary flags
  }
  depends_on = [ /* dependencies on juju controller bootstrap resources */ ]
}

In this example, the local-exec provisioner executes a shell command on the local machine. You'd replace "juju model-defaults ..." with the actual Juju command to set your desired defaults. This includes the controller address, the model name, and any other parameters you want to configure. The depends_on attribute is crucial. It ensures that the provisioner only runs after the necessary resources, such as the Juju controller, are already set up.

Downsides of the local-exec Approach

While this approach gets the job done, it has several significant drawbacks. Primarily, it couples your Terraform configuration to the machine where Terraform is running. This introduces potential issues if you change your infrastructure setup or move your Terraform scripts to a new environment. You must ensure the same dependencies are met. Another significant downside is that local-exec is less declarative than a native resource. It relies on executing commands, making it harder to understand what's being configured and potentially leading to errors. It also doesn't integrate seamlessly with the Terraform provider’s error handling. This means debugging can become tricky if something goes wrong. Finally, managing credentials and ensuring that the executing user has the correct permissions can be more complex with local-exec.

Why a Native Provider Resource Makes Sense

The benefits of a native provider resource for configuring juju model-defaults far outweigh the current workaround. It aligns perfectly with the core principles of infrastructure-as-code. This ensures configurations are manageable, repeatable, and easier to understand. Here's why it's the better way:

Declarative Configuration

A dedicated resource enables a declarative approach to configuration. Instead of defining imperative commands, you simply declare the desired state of your model defaults. Terraform's provider handles the translation of the configuration into the appropriate Juju commands. This declarative style is easier to understand, maintain, and version control.

Improved Error Handling

A native resource can provide improved error handling and reporting. The provider can translate Juju's error messages into user-friendly, actionable feedback. This simplifies debugging and reduces the time required to troubleshoot issues. Instead of manually interpreting the output of shell commands, you get clearer error messages that pinpoint the root cause.

Security Enhancements

The resource can leverage Terraform's existing mechanisms for handling credentials and authentication. This improves security by centralizing the management of access keys and ensuring that credentials are not exposed in the configuration itself. This leads to more secure and controlled access.

Enhanced Version Control

With a dedicated resource, you can easily track changes to your model defaults in version control systems. This enables you to understand when and why configurations were modified and makes it easier to revert to previous states if necessary. This level of traceability is invaluable for maintaining consistency and troubleshooting issues.

Urgency and Context

This is more of a casual wishlist than a critical emergency. There isn't an immediate need for this feature, but it would greatly enhance the user experience when using Terraform with Juju. It would also improve the overall manageability and maintainability of Juju deployments. The request stems from the desire to streamline workflows and remove the complexities associated with using local-exec.

Additional Notes

It's worth noting that the Terraform provider can't currently bootstrap a Juju controller (refer to this issue). However, configuring model defaults on an already bootstrapped controller is certainly a supported and valid use case. The main goal is to provide a more elegant way to handle post-bootstrap operations and manage Juju configurations effectively.

Conclusion: A Better Future for Juju and Terraform

Implementing a native provider resource to configure juju model-defaults would be a significant step forward for the Terraform Juju provider. It aligns with best practices for infrastructure-as-code, improves user experience, and simplifies the management of Juju deployments. While the current local-exec provisioner works, a dedicated resource would bring greater clarity, security, and efficiency to the process. Here's hoping this feature request gains some traction and becomes a reality. Thanks for reading!

For further reading on Juju and Terraform, check out the official documentation and community resources.

External Links:

• Juju Documentation: https://juju.is/docs
• Terraform Documentation: https://www.terraform.io/docs