Reference Variable inside Module

Question

I am trying to reference a variable declared inside a module to update another variable in the same module and i am unable to find a guide as to how i can reference the variable.

Here is my code sippet

module "cluster" {
  source = "..."

  var1 = value1    # directly passing value
  var2 = module.cluster.var1 # I need to update this variable value based on value of var1

I am facing below error during terraform plan

Terraform v1.0.11
on linux_amd64
Configuring remote state backend...
Initializing Terraform configuration...

 Error: Unsupported attribute
│ 
│   on main.tf line 04, in module "cluster":
│   04:       var2 = module.cluster.var1
│     ├────────────────
│     │ module.cluster is a object, known only after apply
│ 
│ This object does not have an attribute named "var1".

I have also tried using referencing using local.var1 shown below

module "cluster" {
  source = "..."

  var1 = value1    # directly passing value
  var2 = local.var1 # I need to update this variable value based on value of var1

and then i encounter below error

Terraform v1.0.11
on linux_amd64
Configuring remote state backend...
Initializing Terraform configuration...
╷
│ Error: Reference to undeclared local value
│ 
│   on main.tf line 04, in module "cluster":
│   04:       var2 = local.var1
│ 
│ A local value with the name "var1" has not been declared.
╵

any lead will be helpful.

Regards

You can both assign and use local values in the locals context, so it's surprising that you can't assign a value and use it in the same module context. There are cases where this forces error-prone duplication -- if you don't opt for the (even worse) external locals definition of the value. — Brent Bradburn
– Brent Bradburn, Commented May 8, 2023 at 23:36

Mark B · Accepted Answer · 2022-01-22 18:14:54Z

5

Your second attempt, using a local variable, is on the right track, but you have to actually declare the local variable:

locals {
   var1 = value1
}

module "cluster" {
  source = "..."

  var1 = local.var1
  var2 = local.var1

answered Jan 22, 2022 at 18:14

Mark B

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