Analyzing the Code Snippets

Oct 13, 2025 by pynkocean.com 102 views

Introduction

When working with Terraform modules, especially those related to IP Address Management (IPAM), it's not uncommon to encounter errors related to the use of sub_pools={}. In this article, we'll delve into the issue of sub_pool={} errors and explore possible solutions to resolve the "invalid value" or "reference to undeclared input variable" errors.

Understanding the Issue

The error message indicates that there's an issue with the pool_config variable, specifically with the cidr and netmask_length values. The error message suggests that either cidr or netmask_length must be defined, but not both. However, in the provided code snippets, both cidr and netmask_length are defined.

Analyzing the Code Snippets

Let's take a closer look at the code snippets provided:

Code Snippet 1

pool_configurations = {
    eu-west-1 = {
      description          = "(name)"
      cidr                 = [var.eu_west_1_cidr_2]
      locale               = "eu-west-1"
      ram_share_principals = [data.aws_organizations_organization.organization.arn]
    }
    sub_pools = {
      cr_pool_1 = {
        description = "eu-west-1-pool-1"
        pool_config = {
          cidr                 = [local.eu_west_1_pool_1]
          ram_share_principals = [data.aws_organizations_organization.organization.arn]
        }
      }
    }

Code Snippet 2

pool_configurations = {
    eu-west-1 = {
      description          = "(name)"
      cidr                 = [var.eu_west_1_cidr_2]
      locale               = "eu-west-1"
      ram_share_principals = [data.aws_organizations_organization.organization.arn]
    }
    sub_pools = {
      cr_pool_1 = {
        description          = "eu-west-1-pool-1"
        cidr                 = [local.eu_west_1_pool_1]
        ram_share_principals = [data.aws_organizations_organization.organization.arn]
      }
    }

In both code snippets, the pool_config variable is defined with cidr and ram_share_principals values. However, the netmask_length value is not defined.

Possible Solutions

Based on the analysis, here are some possible solutions to resolve the "invalid value" or "reference to undeclared input variable" errors:

Define netmask_length value: Add the netmask_length value to the pool_config variable, like this:

pool_config = {
  cidr                 = [local.eu_west_1_pool_1]
  netmask_length      = 18
  ram_share_principals = [data.aws_organizations_organization.organization.arn]
}

Remove pool_config variable: If the pool_config variable is not necessary, remove it altogether. The cidr and ram_share_principals values can be defined directly in the sub_pools block.

sub_pools = {
  cr_pool_1 = {
    description          = "eu-west-1-pool-1"
    cidr                 = [local.eu_west_1_pool_1]
    ram_share_principals = [data.aws_organizations_organization.organization.arn]
  }
}

Use a different syntax: Try using a different syntax for defining the sub_pools block, like this:

sub_pools = {
  cr_pool_1 = {
    description          = "eu-west-1-pool-1"
    pool_configurations = {
      cidr                 = [local.eu_west_1_pool_1]
      ram_share_principals = [data.aws_organizations_organization.organization.arn]
    }
  }
}

Conclusion

The "invalid value" or "reference to undeclared input variable" errors in Terraform modules can be frustrating to resolve. By analyzing the code snippets and understanding the issue, we can try different solutions to resolve the errors. In this article, we explored possible solutions, including defining the netmask_length value, removing the pool_config variable, and using a different syntax. By applying these solutions, we can resolve the errors and successfully create the IPAM module.

Q&A: Resolving sub_pool={} errors in Terraform Modules

Q: What is the cause of the "invalid value" or "reference to undeclared input variable" errors in Terraform modules?

A: The cause of these errors is typically related to the use of sub_pools={} in the Terraform module. When sub_pools={} is used, Terraform expects specific values to be defined, such as cidr and netmask_length. If these values are not defined or are defined incorrectly, Terraform will throw an error.

Q: Why do I get the error "Pool Name: Unamed - must define exactly one of `cidr` or `netmask_length`"?

A: This error occurs when Terraform is expecting either cidr or netmask_length to be defined, but not both. However, in your code, both cidr and netmask_length are defined. To resolve this error, you can either define one of the values and remove the other, or define both values correctly.

Q: How do I define the `netmask_length` value in the `pool_config` variable?

A: To define the netmask_length value in the pool_config variable, you can add the following code:

pool_config = {
  cidr                 = [local.eu_west_1_pool_1]
  netmask_length      = 18
  ram_share_principals = [data.aws_organizations_organization.organization.arn]
}

Q: Can I remove the `pool_config` variable altogether?

A: Yes, if the pool_config variable is not necessary, you can remove it altogether. The cidr and ram_share_principals values can be defined directly in the sub_pools block.

Q: What is the difference between `pool_config` and `pool_configurations`?

A: pool_config and pool_configurations are both used to define the configuration of the pool. However, pool_config is typically used to define the specific configuration of a pool, while pool_configurations is used to define the overall configuration of the pool.

Q: Can I use a different syntax for defining the `sub_pools` block?

A: Yes, you can use a different syntax for defining the sub_pools block. For example:

sub_pools = {
  cr_pool_1 = {
    description          = "eu-west-1-pool-1"
    pool_configurations = {
      cidr                 = [local.eu_west_1_pool_1]
      ram_share_principals = [data.aws_organizations_organization.organization.arn]
    }
  }
}

Q: How do I troubleshoot the "invalid value" or "reference to undeclared input variable" errors in Terraform modules?

A: To troubleshoot these errors, you can try the following:

Check the Terraform documentation for the specific module you are using to ensure that you are using the correct syntax and values.
Review the error message to identify the specific issue.
Try removing or modifying the pool_config variable to see if it resolves the issue.
Try using a different syntax for defining the sub_pools block.

Conclusion

Resolving the "invalid value" or "reference to undeclared input variable" errors in Terraform modules can be challenging. However, by understanding the cause of the error and trying different solutions, you can successfully resolve the issue and create the IPAM module.