The for_each value depends on resource attributes that cannot be determined until apply, so Terraform cannot predict how many instances will be created.

When working with terraform loops you may encounter the error that is shown below.

The “for_each” value depends on resource attributes that cannot be determined until apply, so Terraform cannot predict how many instances will be created.

I faced this particular issue when I tried to dynamically create a azurerm_monitor_diagnostic_setting resource for multiple web apps.

The for_each code is shown below:

resource "azurerm_monitor_diagnostic_setting" "diag_settings_app" {
  depends_on = [ azurerm_windows_web_app.app_service1,azurerm_windows_web_app.app_service2 ]
  for_each = toset(local.app_service_ids)
  name               = "diag-rule"
  target_resource_id = each.value
  log_analytics_workspace_id = local.log_analytics_workspace_id
  
  dynamic "log" {
    iterator = entry
    for_each = local.log_analytics_log_categories
    content {
        category = entry.value
        enabled  = true

        retention_policy {
      enabled = false
        }
    }
   
  }

  metric {
    category = "AllMetrics"

    retention_policy {
      enabled = false
      days = 30
    }
  }

}

The local.app_service_ids defines the app services IDs.

app_service_ids = [azurerm_windows_web_app.app_service1.id,azurerm_windows_web_app.app_service2.id]

In order to override this issue I used count loop instead.

resource "azurerm_monitor_diagnostic_setting" "diag_settings_app" {
  depends_on = [ azurerm_windows_web_app.app_service1,azurerm_windows_web_app.app_service2 ]
  count = length(local.app_service_ids)
  name               = "diag-rule"
  target_resource_id = local.app_service_ids[count.index]
  log_analytics_workspace_id = local.log_analytics_workspace_id
  
  dynamic "log" {
    iterator = entry
    for_each = local.log_analytics_log_categories
    content {
        category = entry.value
        enabled  = true

        retention_policy {
      enabled = false
        }
    }
   
  }

  metric {
    category = "AllMetrics"

    retention_policy {
      enabled = false
      days = 30
    }
  }

}

terraform apply will then work: