Remote state data source for cross-project in Terraform - Step-by-Step Execution

Process Flow - Remote state data source for cross-project

Start Terraform config

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Define remote state backend

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Terraform stores state remotely

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In another project, define data source

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Terraform reads remote state data

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Use remote state outputs in current config

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Apply configuration with cross-project data

Terraform stores state remotely in one project and reads it from another using a remote state data source to share outputs.

Execution Sample

Terraform

data "terraform_remote_state" "network" {
  backend = "gcs"
  config = {
    bucket = "network-state-bucket"
    prefix = "terraform/state"
  }
}

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

This code reads the remote state from a Google Cloud Storage bucket in another project and outputs the VPC ID.

Process Table

Step	Action	Evaluation	Result
1	Terraform reads local config	Detects remote state data source	Prepares to fetch remote state
2	Connect to GCS bucket 'network-state-bucket'	Access remote state file at 'terraform/state'	Remote state file found and read
3	Parse remote state JSON	Extract outputs.vpc_id	vpc_id value obtained (e.g., 'vpc-12345')
4	Assign output 'network_vpc_id'	Set to remote vpc_id value	Output ready for use in current project
5	Apply configuration	Use output value in resources	Resources configured with remote VPC ID
6	End	No errors	Cross-project remote state data successfully used

💡 Remote state data source successfully fetched and used for cross-project reference

Status Tracker

Variable	Start	After Step 3	Final
data.terraform_remote_state.network.outputs.vpc_id	undefined	vpc-12345	vpc-12345
output.network_vpc_id	undefined	undefined	vpc-12345

Key Moments - 3 Insights

Why do we need to specify the backend and config in the remote state data source?

Because Terraform needs to know where and how to access the remote state file. The backend and config tell it the storage location and path, as shown in execution_table step 2.

What happens if the remote state file is missing or inaccessible?

Terraform will fail to read the remote state and throw an error during planning or applying, stopping the process before step 4 in the execution_table.

Can outputs from the remote state be used directly in resource definitions?

Yes, once Terraform reads the remote outputs (step 3), they can be referenced in resource configurations as shown in step 5.

Visual Quiz - 3 Questions

Look at the execution table, at which step does Terraform obtain the remote output value?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Check the 'Evaluation' column for when outputs.vpc_id is extracted.

According to the variable tracker, what is the value of 'output.network_vpc_id' after step 3?

A vpc-12345

B null

C undefined

D empty string

💡 Hint

Look at the 'After Step 3' column for 'output.network_vpc_id' in variable_tracker.

If the GCS bucket name in the config is changed, which step in the execution table would fail?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Step 2 involves connecting to the GCS bucket; changing the bucket name affects this step.

Concept Snapshot

Terraform remote state data source:
- Use 'terraform_remote_state' data block
- Specify backend and config to locate remote state
- Access outputs from remote state
- Enables sharing data across projects
- Must have read access to remote state storage

Full Transcript

This visual execution shows how Terraform uses a remote state data source to read outputs from another project's state file stored remotely, such as in a Google Cloud Storage bucket. The flow starts with Terraform reading the local config, then connecting to the remote backend to fetch the state file. It parses the state to extract outputs like VPC ID, assigns these to local outputs, and uses them in resource definitions. Variables track the output value as it becomes available. Key moments clarify why backend config is needed, what happens if remote state is missing, and how outputs are used. The quiz tests understanding of when values are obtained and what happens if config changes.