How to get internal ip of postgreSQL DB in GCP created by Terraform - postgresql

Question

I am learning terraform deployments coupled with GCP to streamline deployments.
I have successfully deployed a postgreSQL db.
Now I am trying to utilize terraform outputs to write a the private ip generated by the postgreSQL DB server to the output directory where terraform is initiated from.
What is not clear to me is:
(1) The output is defined within the same main.tf file?
(2) Where is the output parameters referenced from? I cannot find the documentation to properly aline. Such I keep getting the error upon applying: Error: Reference to undeclared resource
My main.tf looks like this
resource "google_sql_database_instance" "main" {
name = "db"
database_version = "POSTGRES_12"
region = "us-west1"
settings {
availability_type = "REGIONAL"
tier = "db-custom-2-8192"
disk_size = "10"
disk_type = "PD_SSD"
disk_autoresize = "true"
}
}
output "instance_ip_addr" {
value = google_sql_database_instance.private_network.id
description = "The private IP address of the main server instance."
}

Answer 1

As for the code style, usually there would be a separate file called outputs.tf where you would add all the values you want to have outputted after a successful apply. The second part of the question is two-fold:
You have to understand how references to resource attributes/arguments work [1][2]
You have to reference the correct logical ID of the resource, i.e., the name you assigned to it, followed by the argument/attribute [3]
So, in your case that would be:
output "instance_ip_addr" {
value = google_sql_database_instance.main.private_ip_address # <RESOURCE TYPE>.<NAME>.<ATTRIBUTE>
description = "The private IP address of the main server instance."
}
[1] https://www.terraform.io/language/expressions/references#references-to-resource-attributes
[2] https://www.terraform.io/language/resources/behavior#accessing-resource-attributes
[3] https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/sql_database_instance#attributes-reference

Answer 2

To reference an attribute of a resource, you should put something like:
[resource type].[resource name].[attribute]
In this case, the output should be:
output "instance_ip_addr" {
value = google_sql_database_instance.main.private_ip_address
description = "The private IP address of the main server instance."
}
The output attributes are listed in the documentation. It's fine to put that in main.tf.