scaling_config block causes invalid configuration when defaulted and wrapped in list

[Eliaslis]

Description

When creating a Lambda function with an SQS trigger like the following:

triggers = {
  "trigger" = {
    trigger_type            = "sqs"
    source_arn              = data.aws_sqs_queue.notifier.arn
    function_response_types = ["ReportBatchItemFailures"]
  }
}

If scaling_config is not explicitly defined, it defaults to [].
However, in the module’s main.tf file, the following block is used:

dynamic "scaling_config" {
  for_each = try([each.value.scaling_config], [])
  content {
    maximum_concurrency = try(scaling_config.value.maximum_concurrency, null)
  }
}

This try([each.value.scaling_config], []) causes the value to be wrapped in a list, and when scaling_config is not defined, the for_each receives [{}], which leads to an invalid configuration and triggers an error (see screenshot below).

After modifying the block to not wrap the value in a list, like so:

dynamic "scaling_config" {
  for_each = try(each.value.scaling_config, [])
  content {
    maximum_concurrency = try(scaling_config.value.maximum_concurrency, null)
  }
}

The issue was resolved successfully and the plan returned:

No changes. Your infrastructure matches the configuration.

✋ I have searched the open/closed issues and my issue is not listed.

⚠️ Note

Before submitting this issue:

• Removed the .terraform/ directory

• Re-initialized using terraform init

• Re-tested with terraform apply

Versions

• Module version: 8.0.1

• Terraform version: v1.12.2

• Provider version(s): provider registry.terraform.io/hashicorp/aws v6.4.0

Reproduction Code [Required]

Steps to reproduce:

1. Create a Lambda with a trigger as shown above

2. Do not define scaling_config

3. Use the original block:

for_each = try([each.value.scaling_config], [])

4. Run terraform apply

Expected behavior

Terraform should detect no changes when scaling_config is undefined and safely skip it.

Actual behavior

Terraform tries to create an empty scaling_config {} block which is invalid for this resource.

Terminal Output Screenshot(s)

Additional context

A small change in how for_each is constructed in the dynamic block resolves the issue and avoids unintended creation of an invalid scaling_config.