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Terraform

GCP IAM: Understanding Authoritative and Authoritative Members

By Filip on 10/07/2024

Learn the difference between "authoritative" and "authoritative" IAM member types in Google Cloud Platform and how they impact permissions and resource access.

GCP IAM: Understanding Authoritative and Authoritative Members

Table of Contents

Introduction

In Google Cloud Platform (GCP), Identity and Access Management (IAM) is essential for controlling access to resources. When using infrastructure-as-code tools like Terraform or Pulumi, understanding "authoritative" and "non-authoritative" IAM management is crucial.

Step-by-Step Guide

In Google Cloud Platform (GCP), managing permissions is crucial for controlling access to your resources. You can manage these permissions using Identity and Access Management (IAM). When working with infrastructure-as-code tools like Terraform or Pulumi, you'll encounter the concepts of "authoritative" and "non-authoritative" IAM management. Let's break down these concepts:

Authoritative IAM Management

Think of "authoritative" as setting the absolute rules for who can access your GCP resources. When you manage IAM in an authoritative way, you're telling GCP: "These are the ONLY permissions that should exist. Anything else should be removed."

Here's how it works:

  1. You define the desired state: You specify exactly which users, groups, or service accounts should have what permissions on a resource.
  2. The tool enforces your definition: Tools like Terraform with certain resources will delete any existing permissions that don't match your configuration.
  3. Complete control: This approach gives you strict control, ensuring that no unexpected permissions linger.

Non-Authoritative IAM Management

"Non-authoritative" is a more permissive approach. It's like saying, "I want to add these permissions, but I don't necessarily want to touch any existing ones."

Here's the breakdown:

  1. You define permissions to add: You specify the permissions you want to grant without affecting other existing permissions.
  2. The tool adds, but doesn't remove: The tool will only add the permissions you've defined. It won't delete any existing permissions, even if they're not in your configuration.
  3. Flexibility and potential risks: This approach is flexible but can lead to permission sprawl if not managed carefully.

When to Use Each Approach

  • Authoritative: Use when you need strict control over permissions and want to ensure that only the specified permissions exist. This is common for security-sensitive resources.
  • Non-Authoritative: Use when you want to add permissions without affecting existing ones. This can be useful for collaborating on resources where different teams manage permissions.

Example Scenario

Imagine you have a GCS bucket.

  • Authoritative: You use Terraform to define that only your "data-science-team" group should have read access. Terraform will remove any other existing permissions on the bucket, ensuring only the data science team has access.

  • Non-Authoritative: You use Terraform to grant the "data-analyst" group write access to the bucket. Terraform adds this permission without affecting any other existing permissions on the bucket.

Important Considerations

  • Tools and Resources: The specific behavior of "authoritative" and "non-authoritative" can vary slightly depending on the tool (Terraform, Pulumi, gcloud command-line) and the GCP resource you're managing. Always refer to the documentation for the specific tool and resource.
  • Security Best Practices: It's generally recommended to use the principle of least privilege. Grant only the necessary permissions and regularly review and revoke unnecessary access.

Code Example

The code demonstrates the difference between authoritative and non-authoritative IAM management for a Google Cloud Storage bucket using Terraform. The first example shows authoritative management where only the explicitly defined "data-science-team" group is granted access to the bucket, while any other existing permissions are removed. The second example illustrates non-authoritative management where the "data-analyst" group is granted access without affecting any other existing permissions on the bucket. The choice between these approaches depends on the desired level of control and flexibility required for managing access to the bucket.

Let's illustrate the concepts with Terraform code examples for managing permissions on a Google Cloud Storage (GCS) bucket.

Scenario: We have a GCS bucket named "my-bucket" and want to manage access for two groups: "data-science-team" and "data-analyst".

1. Authoritative IAM Management

resource "google_storage_bucket" "example" {
  name          = "my-bucket"
  location      = "US"
  force_destroy = false
}

resource "google_storage_bucket_iam_member" "data_science_team" {
  bucket = google_storage_bucket.example.name
  role   = "roles/storage.objectViewer"
  member = "group:data-science-team@example.com"
}

Explanation:

  • We define the GCS bucket.
  • We use google_storage_bucket_iam_member to grant the "data-science-team" group the "Storage Object Viewer" role.
  • Crucially, we don't define any other IAM bindings for this bucket. This means Terraform will remove any existing permissions that are not explicitly defined in our code, ensuring only the "data-science-team" has access.

2. Non-Authoritative IAM Management

resource "google_storage_bucket" "example" {
  name          = "my-bucket"
  location      = "US"
  force_destroy = false
}

resource "google_storage_bucket_iam_binding" "data_analyst" {
  bucket = google_storage_bucket.example.name
  role   = "roles/storage.objectCreator"
  members = [
    "group:data-analyst@example.com",
  ]
}

Explanation:

  • We define the GCS bucket.
  • We use google_storage_bucket_iam_binding to grant the "data-analyst" group the "Storage Object Creator" role.
  • Importantly, we are not removing any other existing permissions. If other users or groups had access to the bucket before, they would retain their access even though they are not explicitly defined in this Terraform code.

Key Takeaways:

  • Authoritative management provides strict control by removing any unspecified permissions.
  • Non-authoritative management offers flexibility by adding permissions without affecting existing ones.
  • Choose the approach that aligns with your security requirements and collaboration model.

Remember to consult the official documentation for Terraform and Google Cloud IAM for the most up-to-date information and best practices.

Additional Notes

  • Understanding the implications of each approach is crucial for maintaining a secure and well-managed GCP environment. Authoritative management helps prevent permission sprawl and enforces strict access control, while non-authoritative management offers flexibility but requires careful monitoring.
  • The choice between authoritative and non-authoritative management depends on your specific needs and security posture. Consider factors like the sensitivity of the resources, the size and structure of your team, and your organization's security policies.
  • It's essential to establish clear communication and collaboration practices within your team when managing IAM permissions. This includes defining who is responsible for managing permissions, using consistent naming conventions, and regularly reviewing and auditing permissions.
  • Leverage tools and features provided by GCP and IaC tools to simplify IAM management. This includes using predefined roles, organizing resources with resource hierarchy, and implementing automation for permission provisioning and de-provisioning.
  • Regularly review and update your IAM policies to reflect changes in your environment and requirements. This helps ensure that your permissions remain aligned with your security goals and minimizes the risk of unauthorized access.
  • Consider using tools like Cloud Asset Inventory and Security Command Center to gain visibility into your IAM configurations and identify potential security risks. These tools can help you detect and remediate issues like excessive permissions, unused accounts, and misconfigured access controls.

Remember: IAM is a fundamental aspect of security in GCP. By understanding the concepts of authoritative and non-authoritative management and following best practices, you can effectively control access to your resources and maintain a secure cloud environment.

Summary

Feature Authoritative Non-Authoritative
Definition Sets absolute permissions, removing any not explicitly defined. Adds specified permissions without affecting existing ones.
Control Level Strict Flexible
Process 1. Define desired state.
2. Tool enforces definition, deleting extraneous permissions.
3. Complete control achieved.		 1. Define permissions to add.
2. Tool adds permissions without removing existing ones.
3. Flexibility maintained, potential for permission sprawl.
Use Cases - Security-sensitive resources.
- Enforcing strict access control.		 - Collaboration on resources with shared permission management.
- Adding permissions without disrupting existing access.
Example Granting read access to a GCS bucket only to the "data-science-team" group, removing all other permissions. Granting write access to a GCS bucket to the "data-analyst" group, while preserving existing permissions.
Advantages - Enhanced security.
- Prevents permission creep.		 - Flexibility in collaborative environments.
- Easier to add permissions incrementally.
Disadvantages - Less flexible.
- Requires careful planning to avoid accidental access removal.		 - Potential for permission sprawl.
- Reduced security if not managed diligently.

Important Notes:

  • The specific behavior of authoritative and non-authoritative management can vary depending on the tool (Terraform, Pulumi, gcloud) and the GCP resource.
  • Always consult the relevant documentation.
  • Prioritize the principle of least privilege and regularly review and revoke unnecessary access.

Conclusion

Understanding the difference between authoritative and non-authoritative IAM management in GCP is crucial for maintaining a secure and well-managed cloud environment. Authoritative management enforces strict control over permissions, ensuring only explicitly defined access is granted, while non-authoritative management offers flexibility by adding permissions without modifying existing ones. When to use each approach depends on your specific security requirements, the sensitivity of your resources, and your team's collaborative needs. Regularly review and update your IAM policies, leverage GCP tools for simplified management, and prioritize the principle of least privilege to maintain a secure and well-organized GCP environment.

References

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