CloudNationHQ Psql Azure Module V4.0.0 Bug With Customer Managed Keys

Introduction

Hey guys! We've got a bit of a situation on our hands with the CloudNationHQ psql Azure module, specifically version 4.0.0. It seems there's a bug lurking around how it handles customer-managed keys (CMK). In this article, we're going to dive deep into the issue, break down the problem, and explore how to work around it. If you're using this module, especially with customer-managed keys, you'll want to stick around. We'll be talking about Terraform, Azure, and all the nitty-gritty details. So, let's get started and figure out what's going on!

The Issue: Optional Backup Key Not So Optional

The core of the problem lies in the way the module handles the backup key within the customer_managed_key object. Ideally, this backup key should be entirely optional. You should be able to run your Terraform configurations smoothly even if you only specify a primary key. However, the current implementation throws an error when the backup key isn't provided. This is a major pain point because it forces users to define a backup key even when it's not needed, which goes against the principle of flexibility and optional configurations. The customer-managed keys (CMK) are a critical component for many organizations needing to control their encryption keys for security and compliance reasons. When a module like this doesn't function as expected, it can lead to significant delays and frustrations. This issue particularly affects those who are trying to implement a minimal configuration with just a primary key, highlighting the discrepancy between the intended functionality and the actual behavior of the module.

Technical Deep Dive: Why the Error Occurs

To understand why this error pops up, let's dissect the Terraform code snippet causing the trouble. The issue stems from how the locals.user_assigned_identities are being generated. The code iterates through the customer_managed_key object, expecting both a primary and a backup key. When only the primary key is provided, the iteration still attempts to process the empty backup key. This leads to a null value being accessed, which, in turn, triggers the dreaded “Attempt to get attribute from null value” error. Specifically, lines 2 through 10 of the provided code snippet are the culprits:

 user_assigned_identities = flatten([for uai_key, uai in coalesce(var.instance.customer_managed_key, {}) :
 {
 key = uai_key
 naming_suffix = uai_key == "backup" ? "-bck" : ""
 key_vault_id = uai.key_vault_id
 key_vault_key_id = uai.key_vault_key_id
 } if var.instance.customer_managed_key != null
 ])

This snippet uses a for loop to iterate through the customer_managed_key object. The coalesce function is used to handle cases where the customer_managed_key is null, but it doesn't prevent the loop from attempting to process an empty backup key. The key problem here is that the logic assumes the presence of a backup key if any customer-managed key is defined. When it encounters a null value for uai (because only the primary key is provided), it tries to access attributes like key_vault_id and key_vault_key_id, leading to the error. This is a classic case of code that doesn't handle the absence of an optional parameter gracefully. To fix this, the logic needs to be updated to explicitly check if the backup key is present before attempting to access its attributes. This could involve adding a conditional check within the loop to ensure that only non-null keys are processed.

Reproducing the Bug: A Step-by-Step Guide

If you're curious to see this bug in action (and we encourage you to!), reproducing it is pretty straightforward. All you need to do is run the provided Terraform configuration without defining a backup customer-managed key. Here’s a step-by-step guide:

1. Set up your Terraform environment: Make sure you have Terraform installed and configured with your Azure credentials. This usually involves setting up an Azure service principal and configuring the azurerm provider.
2. Use the problematic module version: Specify version "~> 4.0" of the cloudnationhq/psql/azure module in your Terraform configuration.
3. Define your configuration: Use the provided configuration snippet, ensuring you only define the primary key within the customer_managed_key block. This means you'll specify the key_vault_id and key_vault_key_id for the primary key but leave the backup key undefined.
4. Run terraform init: This command initializes your Terraform working directory, downloading the necessary providers and modules.
5. Run terraform plan: This command will show you the changes Terraform plans to make to your infrastructure. If the bug is present, you'll see the error message we discussed earlier, specifically the “Attempt to get attribute from null value” error.

Here’s the configuration snippet you’ll need:

module "postgresql" {
 source = "cloudnationhq/psql/azure"
 version = "~> 4.0"

 naming = local.naming

 instance = {
 name = module.naming.postgresql_server.name_unique
 location = module.rg.groups.demo.location
 resource_group_name = module.rg.groups.demo.name

 geo_redundant_backup_enabled = true

 customer_managed_key = {
 primary = {
 key_vault_id = module.kv.vault.id
 key_vault_key_id = module.kv.keys.psql.id
 }
 }
 }
}

By following these steps, you can reliably reproduce the bug and confirm that it's indeed the same issue we've been discussing. This hands-on approach is crucial for understanding the problem and validating any potential fixes.

The Error Message: Decoding the Problem

When you run terraform plan with the buggy configuration, you'll be greeted with a rather unfriendly error message. Let's break it down so we know exactly what it's telling us. The key part of the error message looks like this:

Error: Attempt to get attribute from null value

 on .terraform/modules/postgresql/locals.tf line 7, in locals:
 7: key_vault_key_id = uai.key_vault_key_id

This value is null, so it does not have any attributes.

This message is Terraform's way of saying, “Hey, I tried to access something that doesn’t exist!” Specifically, it’s complaining about line 7 in the locals.tf file within the module. This line tries to access the key_vault_key_id attribute of a value (uai) that is null. In simpler terms, the code is expecting a value to be there, but it’s not, causing the program to stumble and throw an error. The error message clearly indicates that the code is trying to access attributes of a null value, which occurs because the backup key is not defined, but the logic still attempts to process it. The preceding line in the error message pinpoints the exact line of code where the problem occurs, making it easier to trace the issue back to the problematic loop we discussed earlier. This level of detail is invaluable when debugging Terraform configurations, as it helps you quickly identify the source of the error and focus your efforts on the relevant part of the code. By understanding the error message, you can better grasp the root cause of the bug and work towards a solution.

Expected Behavior: What Should Happen

The expected behavior here is quite straightforward: Terraform should successfully plan (and apply) even if only the primary customer-managed key is defined. The backup key should be genuinely optional, meaning its absence shouldn't cause the entire process to fail. This aligns with the principle of least configuration, where users only need to specify the parameters that are necessary for their specific use case. In a scenario where a backup key isn't required or desired, the module should gracefully handle this and proceed without errors. The module should ideally provide flexibility for users who have different requirements for key management. Some users might prefer to keep things simple with just a primary key, while others might need the added redundancy of a backup key. The module should cater to both these scenarios seamlessly. When only a primary key is provided, the module should create the PostgreSQL server with customer-managed keys enabled for the primary key without any hiccups. It shouldn't attempt to access attributes of a non-existent backup key, thus avoiding the “Attempt to get attribute from null value” error. This behavior is crucial for ensuring a smooth and predictable user experience, especially in automated infrastructure deployments where errors can lead to significant disruptions.

Possible Solutions and Workarounds

So, what can we do about this bug? While a proper fix would involve updating the module code itself, there are a couple of workarounds we can use in the meantime.

1. Define an Empty Backup Key: The simplest workaround is to explicitly define an empty backup key in your configuration. This satisfies the module's expectation of a backup key being present, even if it doesn't actually point to a key. Your configuration would look something like this:

customer_managed_key = {
 primary = {
 key_vault_id = module.kv.vault.id
 key_vault_key_id = module.kv.keys.psql.id
 }
 backup = {}
}

By providing an empty backup block, you prevent the code from encountering a null value and triggering the error. This is a quick and easy way to bypass the bug without making any changes to the module itself. However, it's important to note that this workaround is just a temporary solution. It doesn't address the underlying issue in the module's logic, and it might not be ideal in all scenarios. For instance, it adds unnecessary configuration to your code, which can make it harder to read and maintain. Additionally, it's possible that future versions of the module might handle empty backup keys differently, potentially breaking this workaround. Therefore, while this approach can get you out of a bind, it's best to keep an eye out for a proper fix in the module itself.

2. Fork the Module and Apply a Fix: For a more robust solution, you could fork the module and implement a fix yourself. This involves creating your own copy of the module's code, modifying it to handle the optional backup key correctly, and then using your forked version in your Terraform configurations. The fix would likely involve adding a conditional check within the for loop to ensure that attributes are only accessed for non-null keys. This could be done using Terraform's can function or by adding an explicit if condition. While this approach requires more effort and a deeper understanding of the module's code, it provides a more permanent solution to the problem. It also gives you greater control over the module's behavior, allowing you to tailor it to your specific needs. However, it's important to keep in mind that maintaining a forked module requires ongoing effort. You'll need to stay up-to-date with changes in the original module and merge them into your fork as needed. Additionally, you'll be responsible for testing and ensuring the stability of your forked version. Despite these challenges, forking the module can be a worthwhile option if you need a reliable solution and are comfortable working with Terraform code.

Conclusion

So, there you have it, guys! We've dissected the bug in the CloudNationHQ psql Azure module, explored why it happens, and discussed some workarounds. It’s crucial to stay informed about these kinds of issues, especially when dealing with critical infrastructure components like customer-managed keys. Whether you choose to use the temporary workaround or dive into forking the module, understanding the problem is the first step toward a solution. Hopefully, the module maintainers will address this issue in a future release, making our lives a little bit easier. Until then, stay vigilant, keep your configurations clean, and happy Terraforming!

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