Introduction
Retrieving the AWS account ID inside Terraform is a recurring requirement when building ARNs, naming resources, or generating policies that reference a known account. Hardcoding the twelve-digit identifier creates brittle configurations that break when credentials change, when work moves across environments, or when the same module is reused in multiple accounts. The aws_caller_identity data source provides a dynamic, credential-aware method to discover the effective Account ID, User ID, and ARN that Terraform is authorized as, without requiring any arguments or manual input.
Why Hardcoding AWS Account ID Fails
Hardcoded account IDs introduce maintenance risk and operational errors.
- 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 an account ID is embedded directly in resource names, bucket policies, IAM policy documents, or ARN strings, a change in AWS profile, role assumption, or target account forces a manual find-and-replace across the codebase. Dynamic retrieval eliminates that manual step and ensures the configuration always reflects the credentials in use during terraform plan and apply.
The awscalleridentity Data Source
Use this data source to get the access to the effective Account ID, User ID, and ARN in which Terraform is authorized.
The data source has no arguments available. It is a zero-configuration lookup that queries the AWS STS identity and returns the caller context for the credentials configured in the AWS provider.
Key takeaways for usage:
- Avoid hardcoding: Instead of manually entering your AWS account ID, use the
aws_caller_identitydata 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.aws_caller_identity.current.account_idvariable throughout your Terraform code, such as in resource names or configurations.
By leveraging the aws_caller_identity data source, you can dynamically retrieve and utilize your AWS account ID within your Terraform projects.
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.
The definition is intentionally empty. The provider uses the active AWS credentials to call STS and populate the attributes.
Accessing and Exporting account_id
Access the account ID and expose it for reuse.
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.
Exporting the value as an output makes the identifier visible after apply and allows other modules or workspaces to reference it without re-querying the data source.
In this example, the account_id is retrieved and displayed as an output.
Practical Usage Patterns
You can use the account_id variable in resource definitions to make your configurations dynamic.
S3 bucket naming example:
hcl
resource "aws_s3_bucket" "example" {
bucket = "example-bucket-${data.aws_caller_identity.current.account_id}"
acl = "private"
}
This configuration creates an S3 bucket with a name that includes the account ID.
ARN construction example:
hcl
source_arn = "arn:aws:events:eu-west-1:${data.aws_caller_identity.current.account_id}:rule/RunDaily"
You can embed the account ID in an ARN like this.
IAM policy use case:
When writing Terraform code, you might need to reference your AWS account ID. Instead of hardcoding this value, it's recommended to use the aws_caller_identity 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 aws_caller_identity data source. This is a more reliable and dynamic approach than hardcoding the ID or fetching it from other sources.
Example bucket with different naming:
hcl
resource "aws_s3_bucket" "my_bucket" {
bucket = "my-bucket-${data.aws_caller_identity.current.account_id}"
# ... other configurations
}
This approach ensures that your Terraform code always uses the correct account ID, even if you switch AWS credentials or environments.
Locals and ARN Construction
Since data.aws_caller_identity.current.account_id is quite long to access every time, it's recommended to store it in a local variable as needed.
hcl
locals {
account_id = data.aws_caller_identity.current.account_id
}
Locals allow a single source of truth and reduce repetition in larger configurations. The local can then be referenced as local.account_id in resource names, tags, and policy documents.
This Terraform code configures the AWS provider and retrieves the caller's AWS account ID. It then uses the account ID to dynamically create an S3 bucket with a unique name.
Attributes of awscalleridentity
The data source returns three attributes that describe the caller.
| Attribute | Description |
|---|---|
| account_id | The AWS Account ID number of the account that owns or contains the calling entity |
| arn | The AWS ARN associated with the calling entity |
| user_id | The unique identifier of the calling entity |
The output can be expressed as:
hcl
output "account_id" {
value = "${data.aws_caller_identity.current.account_id}"
}
output "caller_arn" {
value = "${data.aws_caller_identity.current.arn}"
}
output "caller_user" {
value = "${data.aws_caller_identity.current.user_id}"
}
There are no arguments available for this data source.
Best Practices and Security Implications
Avoid Hardcoding: Always use the aws_caller_identity data source to retrieve the account ID dynamically.
Use Outputs: Export the account_id as an output for reuse in other configurations.
Benefits of dynamic retrieval:
- 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.
The AWS accountid is a unique identifier for your AWS account. In Terraform, you can dynamically retrieve this value using the aws_caller_identity data source. This guide will show you how to use the accountid variable effectively.
The approach ensures that your Terraform code always uses the correct account ID, even if you switch AWS credentials or environments. Other configurations benefit from the same pattern, such as cross-account role assumptions and resource-based policies that must reference a specific account.
Multi-Provider and Multi-Account Considerations
When using multiple AWS providers with different profiles or aliases, the aws_caller_identity data source respects the provider passed to it.
Define a data source named "current" to fetch your caller identity information:
hcl
data "aws_caller_identity" "current" {}
Access and store:
hcl
output "account_id" {
value = data.aws_caller_identity.current.account_id
}
Dynamic usage allows the same module to be applied to multiple accounts without modification. This simplifies configurations for environments spanning multiple AWS accounts and reduces the risk of errors caused by incorrect account IDs.
Conclusion
Dynamic retrieval of the AWS account ID via aws_caller_identity is a foundational pattern for reliable Terraform on AWS. The data source requires no arguments, returns the effective accountid, arn, and userid for the credentials in use, and can be referenced anywhere a static identifier would otherwise be hardcoded.
Using the data source supports dynamic configurations, simplifies multi-account setups, and improves security by reducing manual errors. Exporting the value as an output and optionally caching it in locals makes the identifier reusable across resources, policies, and ARNs.
The recommended workflow is to define data "aws_caller_identity" "current" {}, expose data.aws_caller_identity.current.account_id as an output, and then reference it in resource names, tags, and policy documents. This ensures the configuration always reflects the actual caller context, even when credentials or environments change.