how to use template_file resource in terraform - terraform

Question

I want to launch a 5 VM and as soon as launch it will save the IP of that VM in a file
this is the high level idea of what I want to do I want to launch 5 instance and save all IP in a single VM.
I think here template_file will work but i am not sure how to implement this scenario
i tried
#!/bin/bash
touch myip.txt
private_ip=$(google_compute_instance.default.network_interface.0.network_ip)
echo "$private_ip" >> /tmp/ip.sh
resource "null_resource" "coderunner" {
provisioner "file" {
source = "autoo.sh"
destination = "/tmp/autoo.sh"
connection {
host = google_compute_address.static.address
type = "ssh"
user = var.user
private_key = file(var.privatekeypath)
}
}
connection {
host = google_compute_address.static.address
type = "ssh"
user = var.user
private_key = file(var.privatekeypath)
}
provisioner "remote-exec" {
inline = [
"chmod +x /tmp/autoo.sh",
"sh /tmp/autoo.sh",
]
}
depends_on = ["google_compute_instance.default"]
}
but it is not working as soon as script run through an error as
null_resource.coderunner (remote-exec): /tmp/autoo.sh: line 3: google_compute_instance.default.network_interface.0.network_ip: command not found

Answer 1

There are 2 kinds of template files. One is template_file which is data resouce and the other one is templatefile which is a function.
Template_file is used when you have some file you want to transfer from your machine to provisioning instance and change some paramaters according to that machine. For example:
data "template_file" "temp_file" {
template = file("template.yaml")
vars = {
"local_ip" = "my_local_ip"
}
}
( if you want more detail explanation of what I did in this example just post in the comments but I think it's not for your use case )
This is good because you can change this file for each instance you have if you iterate over it with count for example.
As you can see this template doesn't do what you want to do. It's completely different thing.
To do what you want to it's best to use 2 provisioners:
1st you can use file provisioner to copy the script ( which executes for example ip a, along with some other paramaters to cut and filter only for the data you need )
and 2nd one, remote-exec which will execute that script.
Instead of using depend_on, if you use remote-exec provisioner it's best to use sleep command. Sleep hold you on for given amount of time and let's your instance start properly. You need to choose the right amount of sleep time depending on the size and speed of your instance but I usually do 30 seconds.
I hope I understand your question correctly and hope it helped with something.