Splitting of a map, based on validation - Terraform

Question

I'm looking for a way to split up my config list/map. Reason for this is that we are looking for a way to share resources with other AWS Accounts, by using the aws_ram_principal.

resource "aws_ram_principal_association" "vpc" {
  count = length(module.custom_local.accounts)

  principal          = lookup(module.custom_local.accounts[count.index], "shared") == true ? lookup(module.custom_local.accounts[count.index], "id") : null
  resource_share_arn = aws_ram_resource_share.vpc.arn
}

The module.custom_local.accounts variable looks as followed.

  accounts = [
    {
      "name"   = "account_a",
      "id"     = "111111111111",
      "shared" = false
    },
    {
      "name"   = "account_b"
      "id"     = "222222222222"
      "shared" = true
    },
    {
      "name"   = "account_c"
      "id"     = "333333333333"
      "shared" = true
    }
]

The problem in this is that it works as long as all shared values are true, in case of a false the principal is invalid and complains: The argument "principal" is required, but no definition was found.

Now I was wondering if I can create a local variable that only contains the account ids of the accounts that are true.

Something in the lines of

locals {
  share_accounts = ....
}

Im not sure if this is even possible but my attempts using below didn't get me anywhere.

  share_accounts = { for s in module.custom_local.accounts : s => ... }
- or - 
  share_accounts = [ for index in range(0, length(module.custom_local.accounts) ... ]

Any help is much appreciated - ty.

Answer 1

For statements take a conditional. You could do it like so:

share_accounts = [ for s in module.custom_local.accounts : s if s.shared ]