Get VPC id from another terraform project

Question

I have a terraform project set up an VPC for a region to use for all EKS cluster in that region. After run terraform apply successful, I have these output:

Outputs:

all_worker_mgmt_id = "sg-09992bfxxxx13b782"
azs = tolist([
  "us-east-2a",
  "us-east-2b",
  "us-east-2c",
])
public_subnets = [
  "subnet-03ac0xxxxe533b510",
  "subnet-0f91a04168xxxx9c7",
  "subnet-0xxxxcd5cfcaa938c",
]
vpc_cidr_block = "192.168.0.0/16"
vpc_id = "vpc-07e4xxxxxxxx6f616"

In another terraform project set up an EKS cluster, I need to extract the vpc_id and public_subnets to use to configure the cluster.

How can I dynamic get above variable 's values without hardcode in configuration?

And does this document (https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/vpc) use for that?

Marius Bogdan Marius Bogdan · Accepted Answer · 2021-04-05T09:47:00

I usually keep resources separated in terraform and use data to get the resources that were already created, manually of with other terraform projects.

locals {
  environment = "test"
}

data "aws_vpc" "vpc" {
  filter {
    name = "tag:Name"
    values = [local.environment]
  }
}

data "aws_subnet_ids" "private_subnets" {
  vpc_id = data.aws_vpc.vpc.id

  filter {
    name = "tag:Name"
    values = ["${local.environment}-private-*"]
  }
}

data "aws_subnet_ids" "public_subnets" {
  vpc_id = data.aws_vpc.vpc.id

  filter {
    name = "tag:Name"
    values = ["${local.environment}-public-*"]
  }
}

When you need to get one public or private subnet, use sort:

resource "aws_instance" "gitlab" {
  ...
  subnet_id = sort(data.aws_subnet_ids.public_subnets.ids)[0]
  ...
}

The above code will work perfectly if you use the terraform vpc module

Or, if you want to have a tool that manages all resources at once, you can use Terragrunt

Get VPC id from another terraform project

2 Answers