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AWS Service Control Policies

This guide outlines the process of creating and implementing Amazon Web Services (AWS) Service Control Policies (SCPs) while adhering to Software Development Lifecycle (SDLC) best practices.

 SCPs are a powerful tool for managing permissions across an AWS Organization, but they require careful planning and testing to avoid unintended service disruptions.

Understanding Service Control Policies

Service Control Policies are a type of organization policy that you can use to manage permissions in your organization. SCPs offer central control over the maximum available permissions for all accounts in your organization, allowing you to ensure your accounts stay within your organization's access control guidelines.

Key points:

  • SCPs affect all users and roles in attached accounts, including the root user.
  • SCPs don't grant permissions; they define a guardrail of maximum permissions.
  • SCPs use the same language as IAM policies but have some limitations.

SDLC Best Practices for SCPs

When developing SCPs, follow these SDLC best practices:

  1. Requirements Gathering: Clearly define the purpose of each SCP. Involve stakeholders from security, compliance, and operations teams.
  2. Design: Create a design document outlining the policy structure, affected services, and expected outcomes.
  3. Development: Write the SCP JSON, following AWS best practices and using a consistent style guide.
  4. Version Control: Use a version control system (e.g., Git) to track changes to your SCPs.
  5. Code Review: Implement a peer review process for all SCPs before testing or deployment.
  6. Testing: Thoroughly test SCPs in a non-production environment (more details in section 5).
  7. Documentation: Maintain clear documentation for each SCP, including its purpose, scope, and any exceptions.
  8. Gradual Rollout: Implement SCPs gradually, starting with non-critical accounts or OUs.
  9. Monitoring: Set up monitoring and alerting for SCP-related events and policy violations.
  10. Continuous Improvement: Regularly review and update SCPs based on changing requirements and lessons learned.

Steps to Create an AWS Service Control Policy

Define the Policy Objective: Clearly state what the policy should achieve.

Write the Policy: Use a JSON editor or the AWS Management Console.

Start with the policy structure:

```json
      {
          "Version": "2012-10-17",
          "Statement": [
              {
                  "Sid": "StatementName",
                  "Effect": "Deny",
                  "Action": ["service:Action"],
                  "Resource": "*",
                  "Condition": {}
              }
          ]
      }
      ```

  1. Define the appropriate Effect, Action, Resource, and Condition elements.
  2. Validate JSON Format: Use a JSON validator to ensure correct syntax.
  3. Peer Review: Have another team member review the policy for correctness and unintended consequences.
  4. Document the Policy: Create documentation explaining the policy's purpose, affected resources, and any exceptions.

Testing and Validation

Create a Test Environment

  • Set up a test AWS Organization or use a designated test OU within your existing organization.
  • Ensure the test environment mirrors your production setup as closely as possible.

Policy Simulation

  • Use the IAM Policy Simulator to test the effects of your SCP. 
  • Simulate various user roles and permissions to ensure the SCP behaves as expected.

Controlled Testing

  • Apply the SCP to a test OU or account.
  • Attempt to perform actions that should be allowed and denied by the policy.
  • Verify that the policy doesn't unintentionally restrict necessary operations.

Edge Case Testing

  • Test with different resource types, regions, and account configurations.
  • Ensure the policy doesn't conflict with essential service-linked roles or system operations.

Integration Testing

  • Test the SCP in conjunction with existing IAM policies and other SCPs.
  • Verify that the combination of policies produces the expected permissions.

Performance Impact Assessment

  • Monitor for any performance impacts, especially for policies that use complex conditions.

Rollback Plan

  • Develop and test a rollback plan to quickly remove or modify the SCP if issues are discovered.

Implementing in Production

Gradual Rollout

  • Start by applying the SCP to a small, non-critical OU or set of accounts.
  • Monitor for any issues or unintended consequences.
  • Gradually expand to more critical OUs and accounts.

Communication

  • Inform all relevant teams about the new SCP and its effects.
  • Provide documentation and guidance on working within the new constraints.

Emergency Access Procedure

  • Establish a procedure for emergency access or policy exceptions if needed.

Monitoring and Maintenance

Continuous Monitoring

  • Set up CloudTrail and CloudWatch alerts for policy violations and unexpected denials.
  • Regularly review logs for patterns of policy failures or workarounds.

Regular Reviews

  • Schedule periodic reviews of all SCPs to ensure they remain relevant and effective.
  • Update policies as organizational requirements change.

Feedback Loop

  • Establish a process for users to report issues or request changes to SCPs.
  • Regularly assess the impact of SCPs on productivity and security.

Conclusion

Creating and implementing AWS Service Control Policies is a powerful way to enforce security and compliance across your organization. By following SDLC best practices and thorough testing procedures, you can confidently deploy SCPs that enhance your security posture without disrupting legitimate business operations.

Remember, SCPs are preventive controls and should be part of a comprehensive security strategy that includes detective and responsive measures.