AWS Organizations and Service Control Policies (SCPs)

AWS Organizations is a service that helps you centrally manage and govern your environment as you grow and scale your AWS resources. It allows you to consolidate multiple AWS accounts into an organization that you create and manage. Service Control Policies (SCPs) are a feature of AWS Organizations that you can use to manage permissions in your organization. SCPs are a type of organization policy that you can attach to an organizational unit (OU) or an individual account. SCPs define the maximum permissions that can be delegated to an IAM entity in that account, but they do not grant any permissions themselves.

Understanding AWS Organizations

AWS Organizations enables you to group accounts, apply policies, and manage billing across your AWS footprint. This is crucial for maintaining compliance, controlling costs, and ensuring security best practices across a multi-account strategy. You can organize your accounts into a hierarchical structure of organizational units (OUs) to apply policies more granularly.

AWS Organizations centralizes management of multiple AWS accounts.

It allows you to group accounts, apply policies, and manage billing, which is essential for governance and compliance in a multi-account AWS environment.

AWS Organizations provides a framework for managing multiple AWS accounts. You can create an organization, invite existing accounts, or create new accounts within the organization. The hierarchical structure of OUs allows for the application of policies at different levels, ensuring that governance is applied consistently. This is particularly useful for large enterprises or organizations with distinct teams or projects, each requiring its own AWS account for isolation and management.

Service Control Policies (SCPs): The Guardrails of Your Cloud

SCPs act as a set of guardrails for the permissions that can be used by principals (users or roles) in an account. They define the maximum permissions available to an account, but they do not grant any permissions. Think of them as a 'deny all' policy that you can selectively open up. If an IAM policy allows an action, but an SCP denies it, the action is denied. Conversely, if an IAM policy denies an action, and the SCP allows it, the action is still denied.

Feature	IAM Policies	Service Control Policies (SCPs)
Purpose	Grant specific permissions to users/roles within an account.	Define maximum permissions allowed for principals in an account.
Scope	Account-specific, applied to IAM principals.	Organization-wide or OU-specific, applied to accounts.
Effect	Allow or deny actions.	Deny actions not explicitly allowed (or allow actions not explicitly denied, depending on the SCP structure).
Inheritance	Not directly inherited across accounts.	Inherited down the OU hierarchy.

What is the primary function of Service Control Policies (SCPs) in AWS Organizations?

SCPs define the maximum permissions that can be delegated to an IAM entity within an AWS account, acting as guardrails.

When you create an SCP, you are essentially defining a baseline of what actions are permitted or denied. For example, you could create an SCP that prevents any account in your organization from using the

code

ec2:TerminateInstances

action. Even if an IAM user in that account has a policy that allows them to terminate instances, the SCP will override it, preventing the termination. This is a powerful mechanism for enforcing security and compliance standards.

Imagine a set of nested boxes. The outermost box represents your AWS Organization. Inside, you have smaller boxes for each Organizational Unit (OU), and within those, individual AWS accounts. Service Control Policies (SCPs) are like rules you attach to these boxes. An SCP attached to an OU box applies to all account boxes within it. If an SCP on the OU box says 'No loud noises,' then no account box inside can have loud noises, regardless of what the individual account's internal rules (IAM policies) say. IAM policies are like specific instructions within an account box, granting permissions for specific tasks. The crucial point is that an SCP acts as an upper limit; if an SCP denies an action, it's denied, even if an IAM policy would allow it. Conversely, if an IAM policy denies an action, it's still denied, even if the SCP would allow it. The most restrictive policy wins.

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Applying SCPs: Best Practices

When implementing SCPs, it's recommended to start with a 'least privilege' approach. Begin by denying all actions and then explicitly allow only the necessary services and actions. This ensures that you are not inadvertently granting excessive permissions. You can also leverage AWS managed SCPs, such as the 'FullAWSAccess' or 'DenyAll' policies, as starting points and customize them as needed.

SCPs do not affect the root user of an AWS account. The root user always has full administrative access.

When designing your SCP strategy, consider the different needs of your OUs and accounts. For example, a development OU might have broader permissions than a production OU. You can also use SCPs to enforce compliance requirements, such as restricting access to specific AWS regions or preventing the deletion of critical resources.

Can an SCP grant permissions?

No, SCPs do not grant permissions; they only restrict the maximum permissions that can be delegated by IAM policies.

Key SCP Use Cases

Common use cases for SCPs include:

Restricting access to specific AWS services: Prevent the use of services that are not approved for your organization.
Enforcing regional compliance: Limit resource creation to specific AWS regions.
Preventing accidental deletion: Block actions like
code
```
DeleteBucket
```
or
code
```
TerminateInstances
```
for critical resources.
Controlling billing access: Prevent users from accessing billing information or making changes to the billing configuration.
Enforcing security best practices: Ensure that all resources are deployed with appropriate security configurations.

Summary

AWS Organizations and Service Control Policies are fundamental tools for governing your AWS environment. Organizations provide the structure to manage multiple accounts, while SCPs offer a powerful mechanism to enforce guardrails and control permissions across your organization, ensuring security, compliance, and cost management.

Learning Resources

AWS Organizations User Guide(documentation)

The official AWS documentation providing a comprehensive overview of AWS Organizations, its features, and how to use it.

AWS Service Control Policies (SCPs)(documentation)

Detailed documentation specifically on Service Control Policies, including syntax, examples, and best practices for implementation.

AWS re:Invent 2020: AWS Organizations deep dive(video)

A deep dive session from AWS re:Invent covering advanced topics and best practices for AWS Organizations.

AWS Organizations Best Practices(blog)

A blog post from AWS outlining recommended practices for setting up and managing AWS Organizations effectively.

Understanding the difference between IAM policies and SCPs(blog)

This blog post clarifies the distinct roles and interactions between IAM policies and Service Control Policies.

AWS Certified Solutions Architect - Associate Official Study Guide(paper)

While a book, this study guide often contains sections dedicated to core AWS services like Organizations and SCPs, crucial for certification preparation.

Service Control Policy Examples(documentation)

A collection of pre-written SCP examples that you can adapt for common use cases, such as restricting regions or services.

AWS Organizations Pricing(documentation)

Information on the cost associated with using AWS Organizations, which is generally free for the core features.

AWS IAM Identity Center (successor to AWS SSO) User Guide(documentation)

While not directly SCPs, IAM Identity Center is often used in conjunction with Organizations for centralized user access management, providing context.

AWS Organizations(wikipedia)

A brief overview of AWS Organizations within the broader context of Amazon Web Services on Wikipedia.