Using flatten on a nested map of differing value types

Hi, I’m using terraform v0.12.26 and have a structure very similar to the example on the flatten page, except I have an extra key in the map.

I’m trying to follow the example as closely as possible. I’ve gotten it working using a structure of the same shape, but I’ve had to modify my structure to the following:

<instance_uid> = {
    instance_id = <instance_id>
    vols_list   = [volume_label,volume_label,...]
}

an example being:

instances_vols = {
    "hello_world1" = {
        instance_id = "i-1234"
        vols_list = ["data01","data02","inputs01"]
    }
    "hello_world2" = {
        instance_id = "i-4321"
        vols_list = ["data01","inputs01","outputs01","outputs02"]
    }
}

My plan is to have a resource where I can use a for_each like the following:

for_each = {
    for instance in local.instances_volumes : "${instance.instance_uid}.${instance.volume_label}" => instance
}

and I can then use the values as “each.value.instance_uid” in my resource.

The flattened local looks as follows:

locals {
  instances_volumes = flatten([
    for instance_uid, instance_vol_list in var.instances_vols : [
      for instance_keys, instance_values in instance_vol_list : [
        for vol in instance_keys.vols_list : {
          instance_uid = instance_uid
          instance_id  = instance_keys.instance_id
          volume_label = vol
        }
      ]
    ]
  ])
}

but this doesn’t work, since “for vol in instance_keys.vols_list” doesn’t have any attributes. I’m trying to use the keys my name but this doesn’t seem to work.

The map key “hello_world1” and it’s inner key “instance_uid” are a 1:1 mapping - “hello_world1” would always have an instance_uid of “i-1234” (I mean, it would change in practice, but I could refer to “hello_world1” or “i-1234” and it would be the same thing).

How do I structure my flattened local? Or, can I restructure my input to be more suitable? instances_vols is generated elsewhere as an output to feed into this input, using the following:

output "fileserver_instance_vols" {
    value = {
        for fileserver_module in local.fileserver_modules :
        fileserver_module.uid => {
            instance_id = fileserver_module.instance_id
            vols_list   = fileserver_module.vols_list
        }
    }
}

Is there a better way to structure my output such that it’s much more simple to use as the input later?

Thanks.

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