Terraform_remote_state usage - Mini Project: Build & Apply

Terraform Remote State Usage

📖 Scenario: You are managing infrastructure with Terraform. You want to share outputs from one Terraform project to another safely and efficiently. This is common when you have multiple teams or layers of infrastructure.

🎯 Goal: Build a Terraform configuration that uses terraform_remote_state to access outputs from another Terraform state stored in an S3 bucket.

📋 What You'll Learn

Create a terraform_remote_state data block to read remote state from an S3 backend

Configure the remote state backend with bucket name, key, and region

Access an output variable from the remote state

Use the remote output in a local resource or variable

💡 Why This Matters

🌍 Real World

Terraform remote state is used to share infrastructure information between different teams or layers, such as networking and application layers, without duplicating code or risking inconsistencies.

💼 Career

Understanding terraform_remote_state is essential for cloud engineers and DevOps professionals who manage complex infrastructure with Terraform in collaborative environments.

1

Create terraform_remote_state data block

Create a data block named remote_state of type terraform_remote_state that reads from an S3 backend with the bucket my-terraform-states, key network/terraform.tfstate, and region us-west-2.

Terraform

# Your code here

Hint

Use a data block with type terraform_remote_state and specify the S3 backend configuration inside config.

2

Add a local variable to hold remote output

Add a locals block with a variable named vpc_id that gets the value from data.remote_state.outputs.vpc_id.

Terraform

data "terraform_remote_state" "remote_state" {
  backend = "s3"
  config = {
    bucket = "my-terraform-states"
    key    = "network/terraform.tfstate"
    region = "us-west-2"
  }
}

# Your code here

Hint

Use a locals block and assign vpc_id to the remote state's output value.

3

Use the remote output in a resource

Create a resource aws_subnet named example_subnet that uses local.vpc_id for its vpc_id attribute. Set cidr_block to "10.0.1.0/24" and availability_zone to "us-west-2a".

Terraform

data "terraform_remote_state" "remote_state" {
  backend = "s3"
  config = {
    bucket = "my-terraform-states"
    key    = "network/terraform.tfstate"
    region = "us-west-2"
  }
}

locals {
  vpc_id = data.terraform_remote_state.remote_state.outputs.vpc_id
}

# Your code here

Hint

Define an aws_subnet resource using the local variable vpc_id and set the other attributes as specified.

4

Add provider configuration

Add a provider block for aws with the region set to "us-west-2".

Terraform

data "terraform_remote_state" "remote_state" {
  backend = "s3"
  config = {
    bucket = "my-terraform-states"
    key    = "network/terraform.tfstate"
    region = "us-west-2"
  }
}

locals {
  vpc_id = data.terraform_remote_state.remote_state.outputs.vpc_id
}

resource "aws_subnet" "example_subnet" {
  vpc_id            = local.vpc_id
  cidr_block        = "10.0.1.0/24"
  availability_zone = "us-west-2a"
}

# Your code here

Hint

Define the AWS provider block with the correct region to enable resource creation.

Practice

1. What is the main purpose of using terraform_remote_state in Terraform?

easy

A. To create new resources in the cloud

B. To store Terraform state files locally on your machine

C. To safely share outputs from one Terraform project with another

D. To run Terraform commands faster

Solution

1. Step 1: Understand the role of terraform_remote_state

   The terraform_remote_state data source is used to access outputs from another Terraform state, enabling sharing data between projects.

2. Step 2: Differentiate from other Terraform functions

   It does not store state locally, create resources, or speed up commands; it only reads remote state outputs.

3. Final Answer:

   To safely share outputs from one Terraform project with another -> Option C

4. Quick Check:

   terraform_remote_state shares outputs safely [OK]

Hint: Remember: remote_state reads outputs from other projects [OK]

Common Mistakes:

• Thinking it stores state locally
• Confusing it with resource creation
• Assuming it speeds up Terraform commands

2. Which of the following is the correct syntax to declare a terraform_remote_state data source in Terraform?

easy

A. data "terraform_remote_state" "example" { backend = "s3" config = { bucket = "mybucket" key = "state.tfstate" region = "us-east-1" } }

B. resource "terraform_remote_state" "example" { backend = "s3" config = { bucket = "mybucket" key = "state.tfstate" region = "us-east-1" } }

C. variable "terraform_remote_state" { backend = "s3" config = { bucket = "mybucket" key = "state.tfstate" region = "us-east-1" } }

D. output "terraform_remote_state" { backend = "s3" config = { bucket = "mybucket" key = "state.tfstate" region = "us-east-1" } }

Solution

1. Step 1: Identify correct resource type for remote state

   The terraform_remote_state is declared as a data source, not a resource, variable, or output.

2. Step 2: Check syntax structure

   data "terraform_remote_state" "example" { backend = "s3" config = { bucket = "mybucket" key = "state.tfstate" region = "us-east-1" } } correctly uses data "terraform_remote_state" "example" with backend and config blocks.

3. Final Answer:

   data "terraform_remote_state" "example" { backend = "s3" config = { bucket = "mybucket" key = "state.tfstate" region = "us-east-1" } } -> Option A

4. Quick Check:

   terraform_remote_state is a data source [OK]

Hint: Use 'data' block, not 'resource' for remote_state [OK]

Common Mistakes:

• Using resource instead of data
• Declaring as variable or output
• Missing backend or config blocks

3. Given this Terraform snippet accessing remote state outputs:

data "terraform_remote_state" "network" {
  backend = "s3"
  config = {
    bucket = "net-state"
    key    = "network/terraform.tfstate"
    region = "us-west-2"
  }
}

output "vpc_id" {
  value = data.terraform_remote_state.network.outputs.vpc_id
}

What will be the output value of vpc_id if the remote state has vpc_id = "vpc-123abc"?

medium

A. null

B. "vpc-000000"

C. Error: output not found

D. "vpc-123abc"

Solution

1. Step 1: Understand remote state output access

   The code reads the remote state from S3 bucket and accesses the output named vpc_id.

2. Step 2: Match output value from remote state

   The remote state has vpc_id = "vpc-123abc", so the output will be exactly this string.

3. Final Answer:

   "vpc-123abc" -> Option D

4. Quick Check:

   Remote output vpc_id = "vpc-123abc" [OK]

Hint: Output matches remote state's output value exactly [OK]

Common Mistakes:

• Assuming output is null if not declared locally
• Confusing output with resource ID
• Expecting error if output exists remotely

4. You wrote this Terraform code to read remote state:

data "terraform_remote_state" "app" {
  backend = "s3"
  config = {
    bucket = "app-state"
    key    = "app/terraform.tfstate"
    region = "us-east-1"
  }
}

output "subnet_id" {
  value = data.terraform_remote_state.app.outputs.subnet_id
}

But Terraform shows error: Could not read state file. What is the most likely cause?

medium

A. The output name subnet_id is misspelled in the remote state

B. The S3 bucket or key does not exist or is inaccessible

C. You used resource block instead of data block

D. Terraform version is too old to support remote state

Solution

1. Step 1: Analyze error message

   "Could not read state file" usually means Terraform cannot find or access the remote state file in S3.

2. Step 2: Check configuration and permissions

   Verify the S3 bucket name, key path, and AWS permissions are correct and accessible.

3. Final Answer:

   The S3 bucket or key does not exist or is inaccessible -> Option B

4. Quick Check:

   State file access error means bucket/key issue [OK]

Hint: Check bucket/key existence and permissions first [OK]

Common Mistakes:

• Assuming output name typo causes state read error
• Confusing data block with resource block error
• Blaming Terraform version without checking config

5. You have two Terraform projects: network creates a VPC and outputs vpc_id. app needs to use that vpc_id. How should you configure app to use terraform_remote_state to get vpc_id from network stored in an S3 backend?

hard

A. In app, declare a data "terraform_remote_state" "network" block with backend "s3" and config matching network S3 bucket, key, and region, then access data.terraform_remote_state.network.outputs.vpc_id

B. In app, copy the vpc_id value manually from network outputs and hardcode it

C. In app, declare a resource "terraform_remote_state" "network" block with backend "s3" and config matching network

D. In app, use terraform_remote_state without specifying backend or config

Solution

1. Step 1: Understand cross-project state sharing

   To share outputs, app must declare a data "terraform_remote_state" block with backend and config matching network's S3 backend.

2. Step 2: Access the output properly

   Then app can access vpc_id via data.terraform_remote_state.network.outputs.vpc_id.

3. Final Answer:

   In app, declare a data "terraform_remote_state" "network" block with backend "s3" and config matching network S3 bucket, key, and region, then access data.terraform_remote_state.network.outputs.vpc_id -> Option A

4. Quick Check:

   Use data block with correct backend config to share outputs [OK]

Hint: Use data block with matching backend config to share outputs [OK]

Common Mistakes:

• Hardcoding output values instead of referencing remote state
• Using resource block instead of data block
• Omitting backend or config details