Produce single item maps procedurally from nested map in terraform - terraform

Question

I have a nested map variable of account name and ID by OU, like:
variable "aws_accounts" {
type = map(map(any))
default = {
first_ou = {
first_account = "111111111"
second_account = "222222222"
}
second_ou = {
third_account = "333333333"
fourth_account = "444444444"
}
}
}
This is great for passing a map of account_name to account_id as a sub-variable to do things by ou and the modules in question are constructed to accept a map input.
I would like to also render a local so that I can also reference single accounts but get a map value for them without having to maintain a separate list of variables, like
local.first_account = {
first_account = "111111111"
}
local.second_account = {
second_account = "222222222"
}
local.third_account = {
third_account = "33333333"
}
etc.
I have tried various techniques but without success:
I cannot work out how to refer to each map in the array iteratively- most documentation seems to be based on lists and when I try to do a for_each I get
The "each" object can be used only in "module" or "resource" blocks, and only when the "for_each" argument is set.

Answer 1

Based on your example, it seems like you want to take your two-level map and turn it into a single-level map where the keys are the account names and the "OU names" are just discarded.
Here's one way to achieve that:
locals {
account_ids = merge(values(var.aws_accounts)...)
}
This first uses values to take the values from the top-level map, producing a list of maps.
It then uses merge to take all of the elements from each of the maps and combine them into a single new map. I used the ... symbol to tell Terraform that it should treat each element of the list as a separate argument to merge, rather than just passing the whole list as a single argument.
After merging these together you could potentially split them apart again, creating a separate map each, using a for expression.
locals {
account_maps = tomap({
for k, id in local.account_ids :
k => { (k) = id }
})
}

Answer 2

Maybe not exactly what you're looking for, but could be helpful:
locals {
accounts = merge(var.aws_accounts["first_ou"], var.aws_accounts["second_ou"])
}
If you need to do this in a more dynamic way:
locals {
accounts = zipmap(
flatten([for item in var.aws_accounts : keys(item)]),
flatten([for item in var.aws_accounts : values(item)])
)
}
Now you can access each account with local.accounts["first_account"] etc.

Answer 3

OK So with help from Martin Atkins and Bryan Heden I have found an answer to this. It isn't exactly pretty but it does work:
variable "aws_accounts" {
type = map(map(any))
default = {
first_ou = {
first_account = "111111111"
second_account = "222222222"
}
second_ou = {
third_account = "333333333"
fourth_account = "444444444"
}
}
}
locals {
# gives single map from nested map
account_ids = merge(values(var.aws_accounts)...)
# gives separate structured map for each key
single_accounts_maps = {
for account, id in local.account_ids :
account => {
account = account
id = id
}
}
# gives map where values = keys plus values
single_accounts_maps_joined = zipmap(
flatten([for item in var.aws_accounts : keys(item)]),
[for item in local.single_accounts_maps :
join(" = ", values(item))]
)
# gives nested map by key = {key = "value"}
single_accounts_maps_keys_values = {
for item in local.single_accounts_maps_joined :
(split(" = ", item)[0]) => {
(split(" = ", item)[0]) = (split(" = ", item)[1])
}
}
}
Output that I wanted:
terraform console
> local.single_accounts_maps_keys_values
{
"first_account" = {
"first_account" = "111111111"
}
"fourth_account" = {
"fourth_account" = "444444444"
}
"second_account" = {
"second_account" = "222222222"
}
"third_account" = {
"third_account" = "333333333"
}
}
After the discussion with Martin Atkins and his subsequent edits below, I am recommending his answer instead as simpler, more legible and more graceful, although the tomap() nesting appears to be unneeded, i.e. do
locals {
account_ids = merge(values(var.aws_accounts)...)
account_maps = {
for k, id in local.account_ids :
k => { (k) = id }
}
}