Terraform Variable looping to generate properties - google-cloud-platform

Question

I have to admit, this is the first time I have to ask something that I dont even myself know how to ask for it or explain, so here is my code.
It worth explains that, for specific reasons I CANNOT change the output resource, this, the metadata sent to the resource has to stay as is, otherwise it will cause a recreate and I dont want that.
currently I have a terraform code that uses static/fixed variables like this
user1_name="Ed"
user1_Age ="10"
user2_name="Mat"
user2_Age ="20"
and then those hard typed variables get used in several places, but most importanly they are passed as metadata to instances, like so
resource "google_compute_instance_template" "mytemplate" {
...
metadata = {
othervalues = var.other
user1_name = var.user1_name
user1_Age = var.user1_Age
user2_name = var.user2_name
user2_Age = var.user2_Age
}
...
}
I am not an expert on terraform, thus asking, but I know for fact this is 100% ugly and wrong, and I need to use lists or array or whatever, so I am changing my declarations to this:
users = [
{ "name" : "yo", "age" : "10", "last" : "other" },
{ "name" : "El", "age" : "20", "last" : "other" }
]
but then, how do i get around to generate the same result for that resource? The resulting resource has to still have the same metadata as shown.
Assuming of course that the order of the users will be used as the "index" of the value, first one gets user1_name and so on...
I assume I need to use a for_each loop in there but cant figure out how to get around a loop inside properties of a resource
Not sure if I make myself clear on this, probably not, but didn't found a better way to explain.

Answer 1

From your example it seems like your intent is for these to all ultimately appear as a single map with keys built from two parts.
Your example doesn't make clear what the relationship is between user1 and Ed, though: your first example shows that "user1's" name is Ed, but in your example of the data structure you want to create there is only one "name" and it isn't clear to me whether that name would replace "user1" or "Ed" from your first example.
Instead, I'm going to take a slightly different variable structure which still maintains both the key like "user1" and the name attribute, like this:
variable "users" {
type = map(object({
name = string
age = number
})
}
locals {
# First we'll transform the map of objects into a
# flat set of key/attribute/value objects, because
# that's easier to work with when we generate the
# flattened map below.
users_flat = flatten([
for key, user in var.users : [
for attr, value in user : {
key = key
attr = attr
value = value
}
]
])
}
resource "google_compute_instance_template" "mytemplate" {
metadata = merge(
{
othervalues = var.other
},
{
for vo in local.users_flat : "${vo.key}_${vo.attr}" => vo.value
}
)
}
local.users_flat here is an intermediate data structure that flattens the two-level heirarchy of keys and object attributes from the input. It would be shaped something like this:
[
{ key = "user1", attr = "name", value = "Ed" },
{ key = "user1", attr = "age", value = 10 },
{ key = "user2", attr = "name", value = "Mat" },
{ key = "user2", attr = "age", value = 20 },
]
The merge call in the metadata argument then merges a directly-configured mapping of "other values" with a generated mapping derived from local.users_flat, shaped like this:
{
"user1_name" = "Ed"
"user1_age" = 10
"user2_name" = "Mat"
"user2_age" = 20
}
From the perspective of the caller of the module, the users variable should be defined with the following value in order to get the above results:
users = {
user1 = {
name = "Ed"
age = 10
}
user2 = {
name = "Mat"
age = 20
}
}

Answer 2

metadata is not a block, but a regular attribute of type map. So you can do:
# it would be better to use map, not list for users:
variable "users"
default {
user1 = { "name" : "yo", "age" : "10", "last" : "other" },
user2 = { "name" : "El", "age" : "20", "last" : "other" }
}
}
resource "google_compute_instance_template" "mytemplate" {
for_each = var.users
metadata = each.value
#...
}