Terraform by Example: State Management

1.x

State management is crucial for Terraform. This sample code shows how to use `terraform_remote_state` to read outputs from a separate state file.

Code

data "terraform_remote_state" "network" {
  backend = "s3"

  config = {
    bucket = "my-terraform-state-bucket"
    key    = "network/terraform.tfstate"
    region = "us-east-1"
  }
}

resource "aws_instance" "app" {
  ami           = "ami-12345678"
  instance_type = "t2.micro"
  
  # Use subnet ID from the network state
  subnet_id = data.terraform_remote_state.network.outputs.public_subnet_id
}

Explanation

Terraform uses a state file to map your configuration to real-world resources, track metadata, and improve performance. Proper state management is critical; for team environments, state should always be stored remotely (e.g., in S3) with locking enabled to prevent concurrent modifications and corruption. Storing state in version control is strongly discouraged due to security risks.

The terraform_remote_state data source is a powerful tool for decoupling your infrastructure. It allows one Terraform configuration to read the root-level outputs from another configuration's state file. This enables a layered architecture where, for example, an application layer can consume networking details (like subnet IDs) from a separate networking layer without hardcoding values.

Benefits of remote state include:

Shared Storage: All team members work from the same state file
Locking: Prevents write conflicts during concurrent runs
Security: Encrypts state data at rest and in transit

Code Breakdown

1

data "terraform_remote_state" connects to an external state file.

2

backend = "s3" specifies the type of the remote backend to read from.

4

config block provides the specific credentials and path to the state file.

5

bucket identifies the S3 bucket where the state is stored.

6

key specifies the path to the state file within the bucket.

16

.outputs.public_subnet_id accesses a specific output value from that state.

Samplebadu

Terraform by Example: State Management

Code

Explanation

Code Breakdown