Terraform: Access variables from other modules.

[ashish235]

Hi team,

I 've a root.tf

module "vpc_staging" {
  source = "./vpc_staging"
}


module "security-group" {
  source  = "terraform-aws-modules/security-group/aws"
  version = "1.25.0"

  name = "sg"
  description = "Security group for n/w with needed ports open within VPC"
  vpc_id     = "${module.vpc_staging.vpc_id}"

}

I can very well access the "${module.vpc_staging.vpc_id}" here in this case.

However when I do.

module "vpc_staging" {
  source = "./vpc_staging"
}

module "sg" {
  source = "./sg
}

And the security_group/main.tf has the same configuration as earlier case, it doesn't work.

module "security-group" {
  source  = "terraform-aws-modules/security-group/aws"
  version = "1.25.0"

  name = "sg"
  description = "Security group for n/w with needed ports open within VPC"
  vpc_id     = "${module.vpc_staging.vpc_id}"

}

I get the error

Error: module 'security-group': unknown module referenced: vpc_staging
Error: module 'security-group': reference to undefined module "vpc_staging"

So how do I interpolate variables across modules keeping my root.tf clean?

[aburnett]

If I understand correctly you have a root configuration that uses 2 modules and you want resources from module A to be accessible in module B? In that case you must define values as outputs from module A then pass them in to module B. Variables are not shared globally across modules so values must be defined as outputs or variables for each module.

So in your case in your security-group module should specify vpc_id as a variable. Then in security_group/main.tf would look like:

variable "vpc_id" {}

module "security-group" {
  source  = "terraform-aws-modules/security-group/aws"
  version = "1.25.0"

  name = "sg"
  description = "Security group for n/w with needed ports open within VPC"
  vpc_id     = "${var.vpc_id}"
}

Then in your root.tf you pass it in from your vpc module

module "vpc_staging" {
  source = "./vpc_staging"
}

module "sg" {
  source = "./sg
  vpc_id = "${module.vpc_staging.vpc_id}"
}

[ashish235]

Thanks @aburnett, it worked.

[devshah1012]

How to use if I've some data in other modules and I want to use it in main.tf.

For example,

/modules/network.tf contains below data, and I want to use the output of the show-network in other main.tf

netework.tf

data "network_domain" "network" {
network_domain = "${var.network_domain}"
}

Output the result

output "show-network" {
value = "${data.network_domain. network .network_domains}"
}

main.tf

module "network_domains_data" "getNetworkDomain" {
source = "../module/"

network_domain = "${var.network_domain}"
}

output "listDomains" {

value = // "here I want to use the output of the network.tf"

}

[jayeshjodhawat]

Hello @devshah1012

First of all, you can't have multiple names for a module

To access output available in main.tf, your code should be like this

output "show-network" {
value = "${data.network_domain. network .network_domains}"
}

main.tf

module "network_domains_data" {
source = "../module/"
network_domain = "${var.network_domain}"
}

output "listDomains" {
value = "${module.network_domains_data.show-network}"
}

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