Conditional Execution of Module using Count

Terraform
1

We are getting very strange issue while using count in conjunction with Module. Below code doesn’t instantiate the module even if both the variable values are matching, we tried to assign static value i.e. count = 1, but in that case as well we don’t see the module getting instantiated. Please suggest what could be the possible fix.

Option 1:

module “mymodule” {
source = “./module/sample”
count = var.xyz == var.abc ? 1 : 0
}

Option 2:

module “mymodule” {
source = “./module/sample”
count = 1
}

Both of the above options doesn’t work for me for modules

2

Can you explain what you mean by the following:

Is this that it is not appearing as a resource to add when running a plan or apply, or that it is not provisioning the resources in the module, or something else?

Can you share your output from a plan/apply and can you share a more complete example than above?

Thanks

3

It does not get executed in plan/apply phases, resulting in no resource creation.
Not sure if there is any bug or any setting missing in TF package configuration

4

Without some further example of your Terraform code it is difficult to determine for sure. If you are able to most a minimum reproducible example and also the output of your plan command it may help.
However, two things immediately spring to mind:

  1. You are running your terraform plan/apply from the incorrect folder/directory which contains no terraform files and therefore is treating it as an empty module with nothing to deploy.
    or
  2. At some point you have already applied/deployed this successfully and the module/resources are in your state. Therefore, as Terraform determines there are no changes (or at least changes relevant to the module/resources in question) it will not show the module in a plan or apply (Outside of during the state refresh progress lines). Perhaps run a terraform state list to see if the module/resources are already in your state.
5

Official Terraform 1.8.5 Repo via JARaaS Hybrid RAG - Documentation - code current 6/17/2024

Note: Sources at the end of the response

It appears that you are facing an issue with the conditional instantiation of a module using the count parameter in Terraform. This issue might stem from the way Terraform evaluates the condition and handles the count argument. Here are some potential reasons and fixes for the problem you are experiencing:

Potential Issues:

  1. Variable Definition: Ensure that var.xyz and var.abc are correctly defined and have the expected values.
  2. Parentheses Usage: Sometimes, Terraform might require explicit grouping using parentheses for condition expressions.
  3. Terraform Version: Compatibility issues might arise from different versions of Terraform. Ensure you are using a version that supports this syntax.

Solution Suggestions:

  1. Check Variable Definitions: Ensure that var.xyz and var.abc are defined and their values are what you expect.
variable "xyz" {
  description = "A description for xyz"
  type        = string
}

variable "abc" {
  description = "A description for abc"
  type        = string
}
  1. Using Parentheses: Try adding parentheses around the condition in the count argument.
module "mymodule" {
  source = "./module/sample"
  count  = (var.xyz == var.abc) ? 1 : 0
}
  1. Explicit Boolean Logic: Explicitly compare the values and ensure they are of a compatible type.
module "mymodule" {
  source = "./module/sample"
  count  = (var.xyz == var.abc) ? 1 : 0
}
  1. Terraform Version: Ensure you are using a Terraform version that supports this syntax. Update Terraform to the latest version if necessary.
terraform -v
  1. Trial with Static Value – Confirm Module Instantiation: If count = 1 does not work, there might be another issue preventing module instantiation.

Ensure that the module path and contents are correct.

module "mymodule" {
  source = "./module/sample"
  count  = 1
}
  1. Debug and Log Output: Output the values of var.xyz and var.abc for verification.
output "xyz_value" {
  value = var.xyz
}

output "abc_value" {
  value = var.abc
}

Verification:

  • Run terraform plan to see the evaluated values and to understand what Terraform will apply.
  • Check the debug logs if necessary using TF_LOG=DEBUG terraform apply.

Example Code for Fix Verification:

variable "xyz" {
  description = "A description for xyz"
  type        = string
  default     = "value1"
}

variable "abc" {
  description = "A description for abc"
  type        = string
  default     = "value1"
}

module "mymodule" {
  source = "./module/sample"
  count  = (var.xyz == var.abc) ? 1 : 0
}

output "xyz_value" {
  value = var.xyz
}

output "abc_value" {
  value = var.abc
}

Sources:

Internal Document Reference:

  • Terraform Module Instantiation: terraform_module_instantiation.md (internal document)

Try the suggestions above, and if the issue persists, please provide more details or logs for further troubleshooting.