Introduction

Working with Terraform across AWS environments frequently requires referencing the AWS account ID inside configurations. Hardcoding an account ID creates fragile code that breaks when credentials change, when work moves between development and production accounts, or when Terraform modules are reused across multiple AWS accounts. The reference material consistently recommends a dynamic retrieval approach using the awscalleridentity data source, which queries AWS STS to obtain the caller identity at plan time. This article explains how to retrieve the AWS account ID dynamically, how to expose it as outputs and locals, how to embed it in resource definitions and ARNs, and the operational benefits of avoiding hardcoding. The patterns described are drawn from practical Terraform guidance for dynamic configurations, multi-account setups, and security considerations.

Understanding AWS Account ID in Terraform

The AWS account ID is a unique identifier for your AWS account. In Terraform, you can dynamically retrieve this value using the awscalleridentity data source. This guide will show you how to use the account_id variable effectively.

When writing Terraform, there are times when you need to retrieve and set the AWS account ID, such as when specifying ARNs. This article serves as a reference for how to do this, and also takes a look at the related source code.

Dynamic Configurations: Avoid hardcoding the account ID in your Terraform files.
Multi-Account Setups: Simplify configurations for environments spanning multiple AWS accounts.
Security: Reduce the risk of errors caused by incorrect account IDs.

This is a brief guide on how to retrieve the current AWS account ID in Terraform.

Using awscalleridentity Data Source

To use the AWS accountid variable in Terraform, use the awscaller_identity data source. This allows you to dynamically retrieve the account ID for use in your configurations.

When writing Terraform code, you might need to reference your AWS account ID. Instead of hardcoding this value, it's recommended to use the awscalleridentity data source. This approach provides a more reliable and dynamic way to fetch your account ID within your Terraform scripts.

To use your AWS account ID as a variable in your Terraform code, you should use the awscalleridentity data source. This is a more reliable and dynamic approach than hardcoding the ID or fetching it from other sources.

This Terraform code configures the AWS provider and retrieves the caller's AWS account ID. It then uses the account ID to dynamically create an S3 bucket with a unique name.

Defining the Data Source

Define the data source:
hcl data "aws_caller_identity" "current" {}

This code snippet sets up a data source named "current" that fetches the caller's identity information.

You can retrieve the AWS account ID using the awscalleridentity data source.

```hcl
data "awscalleridentity" "current" {}

You can retrieve the account ID with

data.awscalleridentity.current.account_id

```

The awscalleridentity should be using the AWS STS API, so let's find where STS-related functionality is defined in terraform-provider-aws.

Here it is.

Use the awscalleridentity data source to retrieve the account ID dynamically.

Accessing and Outputting Account ID

Access the account ID:
hcl output "account_id" { value = data.aws_caller_identity.current.account_id }

This part defines an output variable called "account_id" and assigns the value of the account ID retrieved by the data source.

In this example, the account_id is retrieved and displayed as an output.

You can use the account_id variable in resource definitions to make your configurations dynamic.

Key takeaways:

• Avoid hardcoding: Instead of manually entering your AWS account ID, use the awscalleridentity data source for a more reliable and flexible approach.
• Data source definition: Define a data source named "current" to fetch your caller identity information:
  hcl data "aws_caller_identity" "current" {}
• Access and store: Access the account ID from the data source and store it in an output variable:
  hcl output "account_id" { value = data.aws_caller_identity.current.account_id }

Dynamic Usage in Resources

You can now use the data.awscalleridentity.current.account_id variable in your Terraform code wherever you need to reference your AWS account ID. For example, to use it in a resource name:

hcl resource "aws_s3_bucket" "my_bucket" { bucket = "my-bucket-${data.aws_caller_identity.current.account_id}" # ... other configurations }

This approach ensures that your Terraform code always uses the correct account ID, even if you switch AWS credentials or environments.

This configuration creates an S3 bucket with a name that includes the account ID.

hcl resource "aws_s3_bucket" "example" { bucket = "example-bucket-${data.aws_caller_identity.current.account_id}" acl = "private" }

As a usage example, you can embed the account ID in an ARN like this:

hcl source_arn = "arn:aws:events:eu-west-1:${data.aws_caller_identity.current.account_id}:rule/RunDaily"

Dynamic usage: Utilize the data.awscalleridentity.current.account_id variable throughout your Terraform code, such as in resource names or configurations.

The article explains how to dynamically use your AWS account ID within your Terraform code using the awscalleridentity data source.

Storing Account ID in Locals for Reuse

Since data.awscalleridentity.current.account_id is quite long to access every time, it's recommended to store it in a local variable as needed.

hcl locals { account_id = data.aws_caller_identity.current.account_id }

Use Outputs: Export the account_id as an output for reuse in other configurations.

Avoid Hardcoding: Always use the awscalleridentity data source to retrieve the account ID dynamically.

This Terraform code configures the AWS provider and retrieves the caller's AWS account ID.

Multi-Account, Provider Aliases and IAM Policies

The approach ensures that your Terraform code always uses the correct account ID, even if you switch AWS credentials or environments.

My precise use-case is really simple, I am using terraform to build an IAM policy. However, I am building the ARN of a known resource (not created by terraform), and it needs the account id. For no...

When using awscalleridentity and two separate aws providers like this:

hcl provider "aws" { profile = "primary" region = "eu-west-2" version = "> 2.41" } provider "aws" { region = "eu-west-2" profile = "secondary" alias = "profile" version = "> 2.41" } data "aws_caller_identity" "primary" {} data "aws_caller_identity" "profile" { provider = aws.profile }

The data source can be bound to a specific provider alias to retrieve the account ID for a different credential set.

Benefits:

• Accuracy: Ensures the correct account ID is used, even when switching credentials or environments.
• Flexibility: Eliminates the need to manually update the account ID in multiple places.
• Best practice: Promotes cleaner and more maintainable Terraform code.

By leveraging the awscalleridentity data source, you can dynamically retrieve and utilize your AWS account ID within your Terraform projects.

Benefits Comparison

The following table summarizes the operational impact of dynamic retrieval versus hardcoding.

Terraform Enterprise Account Details API Context

Reference material also covers the Terraform Enterprise account API. For user tokens, you can use the user, itself.

GET /account/details

bash curl \ --header "Authorization: Bearer $TOKEN" \ --header "Content-Type: application/vnd.api+json" \ --request GET \ https://app.terraform.io/api/v2/account/details

Example response structure:

json { "data": { "id": "user-V3R563qtJNcExAkN", "type": "users", "attributes": { "username": "admin", "is-service-account": false, "auth-method": "tfc", "avatar-url": "https://www.gravatar.com/avatar/9babb00091b97b9ce9538c45807fd35f?s=100&d=mm", "v2-only": false, "is-site-admin": true, "is-sso-login": false, "email": "[email protected]", "unconfirmed-email": null, "permissions": { "can-create-organizations": true, "can-change-email": true, "can-change-username": true } } } }

Your username and email address can be updated with this endpoint.

PATCH /account/update

This PATCH endpoint requires a JSON object with the following properties as a request.

Conclusion

Dynamic retrieval of the AWS account ID via awscalleridentity is the established best practice for Terraform AWS configurations. Defining data "awscalleridentity" "current" {} provides a single source of truth for the caller identity that is evaluated at plan time. Exposing the value through outputs and locals allows reuse across modules and reduces repetition. Embedding data.awscalleridentity.current.account_id in resource names, bucket names, and ARNs eliminates hardcoding and supports multi-account setups without code changes.

The benefits documented in the reference material are accuracy across credential switches, flexibility without manual updates, and cleaner maintainable code. Avoid hardcoding: Always use the awscalleridentity data source to retrieve the account ID dynamically. Use Outputs: Export the account_id as an output for reuse in other configurations. Dynamic Configurations: Avoid hardcoding the account ID in your Terraform files. Multi-Account Setups: Simplify configurations for environments spanning multiple AWS accounts. Security: Reduce the risk of errors caused by incorrect account IDs.

For IAM policy construction where ARNs for known resources must include the account ID, the dynamic variable ensures correctness even when the target account changes. For provider alias scenarios, binding a separate data source to a specific provider instance returns the correct caller identity per profile.

The pattern remains consistent: define the data source, access data.awscalleridentity.current.account_id, optionally store in locals, and reference throughout the configuration. This approach is reliable, dynamic, and aligns with Terraform best practices for account ID handling.

Sources

1. devops-daily.com
2. nulldog.com
3. developer.hashicorp.com
4. en.bioerrorlog.work