Introduction
Retrieving the AWS account ID inside Terraform is a recurring requirement when building ARNs, naming resources, or enforcing account-bound policies. Hardcoding the twelve-digit account ID creates drift, increases error risk, and breaks portability across environments and credentials. The awscalleridentity data source provides a dynamic, provider-driven method to fetch the caller identity at plan time without manual intervention. This article covers the definition, usage patterns, and best practices for using the account ID variable in Terraform configurations with depth and practical examples.
What the awscalleridentity Data Source Provides
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.
The data source is backed by the AWS STS API and exposes caller identity attributes for the credentials configured for the AWS provider. The common attributes returned are:
| Attribute | Description |
|---|---|
| account_id | The AWS account ID of the caller |
| arn | The ARN of the caller identity |
| user_id | The unique user ID of the caller |
These attributes can be used to construct resource names, ARNs, and policy documents without hardcoding values.
Defining the Data Source
To use the AWS account ID variable in Terraform, use the awscalleridentity data source. This allows you to dynamically retrieve the account ID for use in your configurations.
Define a data source named current to fetch your caller identity information:
hcl
data "aws_caller_identity" "current" {}
This code snippet sets up a data source named current that fetches the caller's identity information. The data source reads the credentials from the active AWS provider configuration, which can be the default provider or an aliased provider.
When you need to work with multiple providers, you can bind the data source to a specific provider:
```hcl
provider "aws" {
profile = "primary"
region = "eu-west-2"
}
provider "aws" {
alias = "profile"
profile = "secondary"
region = "eu-west-2"
}
data "awscalleridentity" "primary" {}
data "awscalleridentity" "profile" {
provider = aws.profile
}
```
This pattern ensures each data source reflects the identity of the correct credentials set.
Outputting and Storing the Account ID
Access and store 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
}
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.
```hcl
data "awscalleridentity" "current" {}
output "accountid" {
value = data.awscalleridentity.current.accountid
}
```
Outputs are useful for reuse in other configurations and for verification during applies. Additional outputs are commonly exposed:
```hcl
data "awscalleridentity" "current" {}
output "accountid" {
value = data.awscalleridentity.current.accountid
}
output "callerarn" {
value = data.awscaller_identity.current.arn
}
output "calleruser" {
value = data.awscalleridentity.current.userid
}
```
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
}
Using locals reduces repetition and simplifies updates.
Dynamic Usage in Resource Names and ARNs
You can use the account_id variable in resource definitions to make your configurations dynamic.
hcl
resource "aws_s3_bucket" "example" {
bucket = "example-bucket-${data.aws_caller_identity.current.account_id}"
acl = "private"
}
This configuration creates an S3 bucket with a name that includes the account ID.
Another common pattern is embedding the account ID in an ARN like this:
hcl
source_arn = "arn:aws:events:eu-west-1:${data.aws_caller_identity.current.account_id}:rule/RunDaily"
This approach ensures that your Terraform code always uses the correct account ID, even if you switch AWS credentials or environments.
The dynamic approach is valuable for IAM policy construction where the ARN of a known resource, not created by Terraform, needs the account id.
hcl
resource "aws_s3_bucket" "my_bucket" {
bucket = "my-bucket-${data.aws_caller_identity.current.account_id}"
}
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.
Multi-Account and Environment Patterns
Benefits of dynamic retrieval include:
- 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.
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.
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.
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.
- Access and store: Access the account ID from the data source and store it in an output variable.
- Dynamic usage: Utilize the data.awscalleridentity.current.account_id variable throughout your Terraform code, such as in resource names or configurations.
By leveraging the awscalleridentity data source, you can dynamically retrieve and utilize your AWS account ID within your Terraform projects.
Hardcoded vs Dynamic Comparison
| Approach | Hardcoded Account ID | Dynamic via awscalleridentity |
|---|---|---|
| Maintenance | Requires manual updates per environment | Automatic per provider credentials |
| Error risk | High risk of wrong account | Low risk, validated by STS |
| Portability | Not portable across accounts | Portable across accounts and profiles |
| Security | Risk of committing secrets | No secrets stored |
Best Practices and Implementation Guidance
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.
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.
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.
Use the variable:
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.
This approach ensures that your Terraform code always uses the correct account ID, even if you switch AWS credentials or environments.
The article explains how to dynamically use your AWS account ID within your Terraform code using the awscalleridentity data source.
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.
Bonus: Reading the Terraform Source Code
Let's take a look at the source code where the awscalleridentity data source is implemented. 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.
Conclusion
Dynamic retrieval of the AWS account ID via awscalleridentity is a foundational pattern for reliable Terraform configurations. Using data "awscalleridentity" "current" {} removes the need to hardcode twelve-digit identifiers, enables safe multi-account and multi-profile workflows, and reduces errors when credentials or environments change. Storing the value in locals and exposing it via outputs improves readability and reuse across modules. Embedding the account ID in resource names, ARNs, and IAM policies ensures consistency and portability without manual updates. Adopting this data source as a standard practice leads to cleaner, more maintainable, and more secure infrastructure code.