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Terraform

Terraform AWS Provider: Unconfigurable Attribute "acl" Error

By Filip on 10/07/2024

Learn how to troubleshoot and resolve the "Value for unconfigurable attribute. Can't configure a value for 'acl': its value will be decided automatically" error in Terraform AWS Provider.

Terraform AWS Provider: Unconfigurable Attribute "acl" Error

Table of Contents

Introduction

When using Terraform with the AWS provider, you might encounter the error message "Value for unconfigurable attribute. Can't configure a value for 'acl': its value will be decided automatically". This error occurs because AWS provider version 4.0.0 and later handle the acl attribute differently than previous versions. This article explains why this error happens and provides solutions to resolve it.

Step-by-Step Guide

The error message "Value for unconfigurable attribute. Can't configure a value for 'acl': its value will be decided automatically" when using the AWS provider in Terraform arises from changes introduced in version 4.0.0 of the provider. Prior versions allowed setting the acl attribute directly for resources like aws_s3_bucket. However, version 4 and later determine the ACL automatically based on other configurations.

To resolve this, you should:

  1. Remove the acl attribute: Since the acl attribute is no longer configurable directly, delete it from your aws_s3_bucket resource block in your Terraform code.

  2. Use aws_s3_bucket_acl resource: If you need to manage the bucket ACL separately, use the aws_s3_bucket_acl resource. This resource allows you to define granular access control settings for your bucket.

  3. Upgrade your Terraform configuration: If you're encountering this error after upgrading your AWS provider to version 4 or later, ensure that your Terraform configuration is compatible with the new version. Refer to the upgrade guide for detailed information on breaking changes and how to update your code.

By following these steps, you can fix the "Value for unconfigurable attribute" error and ensure that your Terraform code works correctly with the latest AWS provider version.

Code Example

This code snippet demonstrates how to resolve an error encountered after upgrading the AWS provider for Terraform from version 3.x to 4.x. The error occurs because the acl attribute within the aws_s3_bucket resource is deprecated in version 4.x. The solution involves either removing the acl attribute altogether, allowing the provider to manage it automatically, or using the dedicated aws_s3_bucket_acl resource for explicit ACL control. This example highlights the importance of consulting upgrade guides and migrating configurations when dealing with major version changes in providers.

Scenario: You have an existing Terraform code using AWS provider version 3.x that defines an S3 bucket with a custom ACL:

# Using AWS provider version 3.x
resource "aws_s3_bucket" "example" {
  bucket = "my-example-bucket"
  acl    = "private" 
}

Error: After upgrading to AWS provider version 4.x, running terraform apply throws the error:

Error: Value for unconfigurable attribute
│ 
│   on main.tf line 3, in resource "aws_s3_bucket" "example":
│    3:   acl    = "private"
│ 
│ Can't configure a value for "acl": its value will be decided automatically.

Solution:

  1. Remove the acl attribute:

    # Using AWS provider version 4.x
resource "aws_s3_bucket" "example" {
  bucket = "my-example-bucket"
}

  2. Use aws_s3_bucket_acl resource (if needed):

    # Using AWS provider version 4.x
resource "aws_s3_bucket" "example" {
  bucket = "my-example-bucket"
}

resource "aws_s3_bucket_acl" "example" {
  bucket = aws_s3_bucket.example.id
  acl    = "private"
}

Explanation:

  • In version 4.x, the acl attribute within aws_s3_bucket is deprecated and automatically managed.
  • Removing the acl attribute lets the provider handle it based on other configurations.
  • If you need specific ACL control, use the dedicated aws_s3_bucket_acl resource.

Important:

  • Always consult the AWS provider upgrade guide for potential breaking changes and recommended migration steps when upgrading to a new major version.
  • This example focuses on the aws_s3_bucket resource, but the principle applies to other resources where the acl attribute might be deprecated in favor of dedicated resources.

Additional Notes

  • Impact of removing acl: In most cases, removing the acl attribute won't negatively impact your infrastructure. AWS has good default security settings, and the provider will likely choose a secure configuration. However, it's crucial to understand the implications for your specific use case, especially if you relied on specific ACL settings in the past.
  • When to use aws_s3_bucket_acl: Use this resource only if you require granular control over bucket access beyond what the provider automatically configures. Overusing it can add complexity to your Terraform code.
  • Alternatives to ACLs: Consider using S3 bucket policies for more flexible and powerful access control. Bucket policies offer greater granularity and can manage access based on various factors beyond user and group permissions.
  • Testing after upgrades: After upgrading your AWS provider and modifying your code, thoroughly test your infrastructure to ensure that the changes haven't introduced any unexpected behavior or access issues.
  • Staying up-to-date: Regularly check for new AWS provider releases and consult the upgrade guides. This proactive approach helps you stay ahead of breaking changes and leverage new features and improvements.
  • Community resources: The Terraform and AWS communities are valuable resources for troubleshooting and guidance. Online forums, documentation, and blog posts can provide insights and solutions to common problems.

Summary

This error occurs when using Terraform's AWS provider version 4.0.0 or later and attempting to directly set the acl attribute for resources like aws_s3_bucket. This is because AWS provider v4+ automatically manages the ACL based on other configurations.

Resolution:

  • Remove acl attribute: Delete the acl attribute from your aws_s3_bucket resource block.
  • Use aws_s3_bucket_acl resource: For separate bucket ACL management, utilize the dedicated aws_s3_bucket_acl resource.
  • Upgrade Terraform configuration: Ensure your Terraform configuration is compatible with the newer AWS provider version (v4+). Consult the upgrade guide for breaking changes and code update instructions.

Conclusion

In conclusion, the "Value for unconfigurable attribute" error related to the acl attribute in Terraform's AWS provider version 4.0.0 and later stems from significant changes in how ACLs are managed. By understanding these changes and implementing the provided solutions—removing the deprecated acl attribute or utilizing the dedicated aws_s3_bucket_acl resource—you can ensure your Terraform code remains compatible and functional. Remember to consult the AWS provider upgrade guide for comprehensive information on breaking changes and recommended migration steps when upgrading to newer versions. Staying informed about these updates and adapting your configurations accordingly will lead to a smoother and more efficient infrastructure automation experience with Terraform and AWS.

References

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