Terraform_remote_state usage - Step-by-Step Execution

Process Flow - Terraform_remote_state usage

Define remote state backend

↓

Configure remote state data source

↓

Terraform init to connect backend

↓

Terraform apply to read remote state

↓

Use remote state outputs in current config

↓

Deploy infrastructure with shared data

Terraform remote state usage involves configuring a backend to store state, then accessing that state from another configuration to share data.

Execution Sample

Terraform

terraform {
  backend "s3" {
    bucket = "my-tf-state"
    key    = "app/terraform.tfstate"
    region = "us-east-1"
  }
}
data "terraform_remote_state" "network" {
  backend = "s3"
  config = {
    bucket = "my-tf-state"
    key    = "network/terraform.tfstate"
    region = "us-east-1"
  }
}
output "vpc_id" {
  value = data.terraform_remote_state.network.outputs.vpc_id
}

This code configures an S3 backend for remote state and accesses outputs from a remote state named 'network'.

Process Table

Step	Action	Terraform Command	State Accessed	Result
1	Define backend in terraform block	terraform init	No previous state	Backend configured to S3 bucket
2	Initialize terraform with backend	terraform init	No previous state	Backend connection established
3	Apply network config to create resources	terraform apply	Remote state created	Network resources created, state saved remotely
4	Configure terraform_remote_state data source	terraform plan	Reads remote state from S3	Remote outputs available for use
5	Use remote outputs in current config	terraform apply	Reads remote state	Current config uses remote VPC ID
6	Deploy current infrastructure	terraform apply	Remote state accessed	Resources created using remote state data
7	End	-	-	Execution complete, remote state shared successfully

💡 Terraform completes apply after accessing remote state outputs successfully.

Status Tracker

Variable	Start	After Step 3	After Step 5	Final
backend_configured	false	true	true	true
remote_state_accessible	false	false	true	true
vpc_id	null	set in remote state	read from remote state	used in current config

Key Moments - 3 Insights

Why do we run 'terraform init' before accessing remote state?

Because 'terraform init' sets up the backend connection, allowing Terraform to read or write remote state as shown in execution_table step 2.

How does Terraform know where to find the remote state?

The remote state data source is configured with backend details (bucket, key, region), so Terraform reads the state from that location as in step 4.

What happens if the remote state is not accessible during 'terraform apply'?

Terraform will fail to read required outputs, causing the apply to error out, since it depends on remote state data as in step 5.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does Terraform first access the remote state outputs?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Check the 'State Accessed' column in execution_table rows for when remote state is read.

According to variable_tracker, when does 'remote_state_accessible' become true?

A After Step 3

B At Start

C After Step 5

D Never

💡 Hint

Look at the 'remote_state_accessible' row in variable_tracker to see when it changes.

If the backend configuration was missing, what would happen at Step 2?

A Terraform init would succeed without backend

B Terraform init would fail to connect backend

C Terraform apply would create resources anyway

D Remote state would be accessible

💡 Hint

Refer to execution_table Step 2 where backend connection is established.

Concept Snapshot

Terraform remote state usage:
- Configure backend in terraform block (e.g., S3 bucket)
- Run 'terraform init' to set backend
- Use 'terraform_remote_state' data source to read outputs
- Access remote outputs as variables
- Enables sharing state between configs
- Must ensure backend is accessible before apply

Full Transcript

Terraform remote state usage involves setting up a backend to store the state file remotely, such as in an S3 bucket. First, you define the backend configuration in the terraform block and run 'terraform init' to initialize the backend connection. Then, after applying the initial configuration to create resources and save state remotely, you configure a terraform_remote_state data source in another configuration to read outputs from that remote state. This allows sharing data like VPC IDs between different Terraform projects. The process requires the backend to be accessible during 'terraform apply' to successfully read remote outputs and deploy dependent resources.

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