Output value is not found

[zli82016]

SDK version

github.com/hashicorp/terraform-plugin-sdk/v2 v2.33.0

Relevant provider source code

https://github.com/hashicorp/terraform-provider-google/blob/main/google/services/compute/data_source_google_compute_instance.go#L18

Terraform Configuration Files

resource "google_compute_instance" "test-vm-1" {
  name         = "test-vm-10111701"
  machine_type = "n2-standard-2"
  zone         = "us-central1-a"

allow_stopping_for_update = true

  metadata = {
    foo = "bar"
  }

  boot_disk {
    initialize_params {
      image = "ubuntu-os-cloud/ubuntu-2204-lts"
    }
  }

  network_interface {
    network = "default"
    access_config { }
  }

  service_account {
    email = data.google_compute_default_service_account.default.email
    scopes = [
                "https://www.googleapis.com/auth/logging.write",
            "https://www.googleapis.com/auth/monitoring.write",
    ]
  } 
    
metadata_startup_script = <<-EOT
    #!/bin/bash
    # Update and install necessary packages
    sudo su
    sudo apt update && sudo apt upgrade -y
  EOT 
      
}   

data "google_compute_instance" "iavm_node" {
  name = "${google_compute_instance.test-vm-1.name}"
  zone = "${google_compute_instance.test-vm-1.zone}"
}
  
output "instance_id" {
  value = "${data.google_compute_instance.iavm_node.self_link}"
}

Debug Output

Expected Behavior

terraform output instance_id shows the value of self_link

Actual Behavior

terraform output instance_id
╷
│ Warning: No outputs found
│

But self_link has the value with the command terraform state show data.google_compute_instance.iavm_node

data "google_compute_instance" "iavm_node" {
    self_link                  = "https://www.googleapis.com/compute/v1/projects/xxxx/zones/us-central1-a/instances/test-vm-10111701"
}

Steps to Reproduce

1. terraform apply

Question

How the output value is evaluated here and what is the reason that the output value doesn't have value?

self_link is an optional field in the data source google_compute_instance. I am not sure if that is the reason.

[austinvalle]

Hey there @zli82016 👋🏻 , thanks for reporting the issue and sorry you're running into trouble here.

I think your issue is more related to how Terraform CLI outputs are evaluated, so the Terraform core repo would be a more appropriate place: https://github.com/hashicorp/terraform/issues .

That being said, it does seem possible that the self_link attribute being Optional and not Optional + Computed could affect how Terraform evaluates the expression (since data.google_compute_instance.iavm_node.self_link is Optional and not defined in configuration, the value really should always be null).

I can't transfer your issue directly, but if you open a new issue at https://github.com/hashicorp/terraform/issues , one of the Terraform core engineers may be to confirm what exactly is occurring with the output evaluation.