How can I output and reuse resource IDs from a for_each-called Terraform module in AzureRM?

Below is one common cause and solution for the errors you’re seeing.

What’s Happening

You are using a for‑each on the module call so that each instance of the module creates one Synapse SQL pool. However, within the module you are writing:

HCLCopied
output "synapse_sql_pool_ids" {
  value = values(azurerm_synapse_sql_pool.synapse_sql_pool).*.id
}

Terraform expects that azurerm_synapse_sql_pool.synapse_sql_pool is a collection (like when you also use for_each at the resource level). In your case the resource block creates only one object per module instance. As such, Terraform sees azurerm_synapse_sql_pool.synapse_sql_pool as a singular resource (a primitive object) and then trying to use functions like values() and splat expression (*.id) causes the errors:

• “Unsupported attribute … Can't access attributes on a primitive‑typed value (string)”
• “Missing map element … This map does not have an element with the key 'id'”

The Fix

Since each module creates one SQL pool, you can simply output the id directly. In your module, change the output to:

HCLCopied
output "synapse_sql_pool_id" {
  value = azurerm_synapse_sql_pool.synapse_sql_pool.id
}

Adjusting Usage in Your Root Module

Now that each module instance produces a single synapse_sql_pool_id, your module block outputs a map of these ids keyed by the key in your for_each. For example, if your module call was:

HCLCopied
module "create_synapse_pools" {
  depends_on            = [module.create_synapse]
  source                = "../../resource_modules/synapse_pool"
  for_each              = { for obj in var.synapse_pools : obj.name => obj }
  name                  = each.value.name
  synapse_pool_sku_name = each.value.sku_name
  ...
}

Then the output will be available as a map:

HCLCopied
module.create_synapse_pools["poolA"].synapse_sql_pool_id

If you want to loop over these ids in your next module, you can do something like:

HCLCopied
module "grant_rbac_on_pools_to_automation_account" {
  source   = "../../resource_modules/role_assignment"
  for_each = { for key, mod in module.create_synapse_pools : key => mod.synapse_sql_pool_id }
  ...
}

This ensures that each instance of the role assignment module receives a single resource id.

Summary

• Error Cause: Using values(...).* on a single resource instance instead of a collection.
• Solution: Output the id directly with azurerm_synapse_sql_pool.synapse_sql_pool.id in your module.
• Next Steps: Adjust the for_each in modules that consume this output so that they work with a map of string values.

This change should resolve the errors you are seeing.