How to import resources in Stacks

As described  in our official documentation, resources can be imported into a stack. This article provides a quick-to-use configuration that allows you to import existing resources into a stack-based setup.

Expected Outcome

An existing resource is successfully imported into the Terraform state associated with a stack deployment.

Prerequisites 

• An existing deployed stack in HCP Terraform
• If the stack is not already deployed, refer this document to deploy a stack first 

Use Case

• Assume we already have a stack configured in HCP Terraform with the following directory structure:

├── components
│   └── microservice
│       ├── data.tf
│       ├── locals.tf
│       ├── main.tf
│       ├── variables.tf
│       └── import.tf
├── components.tfcomponent.hcl
├── deployments.tfdeploy.hcl
├── locals.tfdeploy.hcl
├── providers.tfcomponent.hcl
└── variables.tfcomponent.hcl

• The component source is ./components/microservice
• The stack has multiple deployments (for example, dev and prod)
• Each deployment should import a different existing S3 bucket

Procedure:

We can define below configuration and push the code:

Deployment Configuration(deployments.tfdeploy.hcl): Define deployment-specific inputs:

deployment "dev" {
  inputs = {
    ..
    bucket_name = "<name-for-dev>"
    ..
  }
}

deployment "prod" {
  inputs = {
    ..
    bucket_name = "<name-for-prod>"
    ..
  }
}
 

Component Input Variable (variables.tfcomponent.hcl):Declare the variable that will be passed into the component:

variable "bucket_name" {
  type = string
}

Component Definition (components.tfcomponent.hcl): Reference the component source and pass the deployment input:

component "instance" {
  source = "./components/microservice"

  inputs = {
    bucket_name = var.bucket_name
    # other inputs
  }
}

Resource and Import Configuration(import.tf (inside ./components/microservice)): Define the resource and the import block:

variable "bucket_name" {}

resource "aws_s3_bucket" "example" {
  bucket = var.bucket_name
}

import {
  to = aws_s3_bucket.example
  id = var.bucket_name
}

 
With this setup, you can reuse the same component while importing different S3 buckets per deployment by simply changing the bucket_name input in each environment (dev/prod).

Additional Information

• Managing resources in components:https://developer.hashicorp.com/terraform/language/stacks/component/manage#manage-resources
• Terraform import blocks: https://developer.hashicorp.com/terraform/language/import