Retrieving the AWS account ID dynamically inside Terraform is a foundational pattern for building portable, credential-aware infrastructure. Hardcoding a twelve-digit account ID creates drift when you move between development, staging, production, or multiple AWS accounts. The awscalleridentity data source provides a read-only view of the identity Terraform is currently authorized with, allowing the account ID, ARN, and user ID to be consumed directly in resource names, ARNs, and policy documents without manual updates.
Why Dynamic Account ID Matters
Writing Terraform code that references your AWS account ID becomes necessary when you need to construct ARNs for existing resources, enforce cross-account permissions, or create resource names that are globally unique per account. Hardcoding the ID introduces risk of errors caused by incorrect account IDs, breaks portability across environments, and forces manual edits when credentials or environments change.
Using the awscalleridentity data source enables dynamic configurations that avoid hardcoding the account ID in Terraform files. It simplifies configurations for environments spanning multiple AWS accounts and reduces the risk of errors caused by incorrect account IDs. The approach ensures Terraform code always uses the correct account ID, even if you switch AWS credentials or environments.
awscalleridentity Data Source Overview
The data source is used to get access to the effective Account ID, User ID, and ARN in which Terraform is authorized. There are no arguments available for this data source.
The attributes exposed by the data source are:
| 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 data source relies on AWS STS API functionality to resolve the caller identity. It is a read-only data source with no configuration arguments.
Defining the Data Source
A minimal definition fetches the caller identity information under a name such as current.
hcl
data "aws_caller_identity" "current" {}
This code snippet sets up a data source named current that fetches the caller's identity information. Once defined, the data source can be referenced throughout the configuration as data.awscalleridentity.current.
Accessing Attributes and Outputs
After defining the data source, the account ID can be surfaced as an output for reuse in other configurations.
hcl
output "account_id" {
value = data.aws_caller_identity.current.account_id
}
In this example, the account_id is retrieved and displayed as an output. Additional outputs for ARN and user can be defined similarly:
```hcl
output "callerarn" {
value = "${data.awscaller_identity.current.arn}"
}
output "calleruser" {
value = "${data.awscalleridentity.current.userid}"
}
```
Exporting the account_id as an output makes it available to other modules and to operators for verification.
Storing in Locals for Reuse
Because data.awscalleridentity.current.account_id is lengthy to access repeatedly, it is recommended to store it in a local variable as needed.
hcl
locals {
account_id = data.aws_caller_identity.current.account_id
}
The local can then be used in resource definitions and expressions, improving readability and reducing repetition.
Using Account ID in Resource Names
The account ID can be interpolated into resource names to make configurations dynamic.
hcl
resource "aws_s3_bucket" "example" {
bucket = "example-bucket-${data.aws_caller_identity.current.account_id}"
acl = "private"
}
This configuration creates an S3 bucket with a name that includes the account ID.
Another example:
hcl
resource "aws_s3_bucket" "my_bucket" {
bucket = "my-bucket-${data.aws_caller_identity.current.account_id}"
}
This approach ensures that your Terraform code always uses the correct account ID, even if you switch AWS credentials or environments. It also ensures the correct account ID is used, even when switching credentials or environments.
Dynamic ARN Construction
A common use case is building ARNs for known resources not created by Terraform, such as IAM policies referencing event rules.
hcl
source_arn = "arn:aws:events:eu-west-1:${data.aws_caller_identity.current.account_id}:rule/RunDaily"
When writing Terraform code, there are times when you need to retrieve and set the AWS account ID, such as when specifying ARNs. Embedding the account ID dynamically avoids manual updates when the account changes.
Dynamic Configurations and Multi-Account Setups
The data source supports dynamic configurations that avoid hardcoding the account ID in your Terraform files. It simplifies configurations for environments spanning multiple AWS accounts.
Key takeaways for adoption:
- 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.
Benefits 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.
By leveraging the awscalleridentity data source, you can dynamically retrieve and utilize your AWS account ID within your Terraform projects.
Best Practices for Implementation
- 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 once per configuration to avoid repeated calls.
- Use locals for repeated interpolation to keep code readable.
The AWS accountid is a unique identifier for your AWS account. In Terraform, you can dynamically retrieve this value using the awscalleridentity data source. This guide shows how to use the accountid variable effectively.
Conclusion
Retrieving the AWS account ID via awscalleridentity is a reliable and dynamic way to fetch your account ID within Terraform scripts. The data source provides accountid, arn, and userid without arguments, and the value can be used directly in resource names, locals, outputs, and ARN construction. Avoiding hardcoding improves accuracy across credential switches and environments, supports multi-account setups, and reduces errors caused by incorrect account IDs. Defining data "awscalleridentity" "current" {} once and referencing data.awscalleridentity.current.account_id throughout the configuration promotes portable, maintainable infrastructure as code. Using outputs and locals further improves reuse and clarity when the account ID must be shared across modules or constructed into complex identifiers.