AWS SCP

AWS Service Control Policies (SCPs) are a component of AWS Organizations that enable centralized control over permissions and resource usage across multiple AWS accounts. In the context of FinOps, SCPs play a vital role in managing costs and enforcing financial governance within cloud environments.

Key Features and Functionality

Policy Structure and Syntax

SCPs use JSON syntax similar to IAM policies. They consist of:

• Version: Specifies the policy language version

• Statement: Contains one or more individual statements

Each statement includes:

• Effect: “Allow” or “Deny”

• Action: AWS service actions

• Resource: AWS resources to which the actions apply

Inheritance and Hierarchy

SCPs follow the AWS Organizations hierarchy:

• Root: Applies to all accounts in the organization

• Organizational Unit (OU): Applies to accounts within the OU

• Account: Applies directly to individual accounts

Policies are inherited down the hierarchy, with child OUs and accounts subject to all policies from parent levels.

Denylist vs. Allowlist Approach

SCPs can be implemented using two approaches:

1. Denylist: Allow all actions by default, then explicitly deny specific actions

2. Allowlist: Deny all actions by default, then explicitly allow specific actions

The choice between these approaches depends on an organization’s security posture and operational requirements.

Integration with IAM Policies

SCPs work in conjunction with IAM policies:

• SCPs set the upper limit of permissions

• IAM policies grant specific permissions within those limits

This layered approach provides granular control over user and role permissions while maintaining organizational-level restrictions.

Implementing SCPs for Cost Control

Limiting Resource Creation

SCPs can restrict the creation of costly resources:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "ec2:RunInstances"
      ],
      "Resource": "*",
      "Condition": {
        "StringEquals": {
          "ec2:InstanceType": ["x1.32xlarge", "p3.16xlarge"]
        }
      }
    }
  ]
}

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "ec2:RunInstances"
      ],
      "Resource": "*",
      "Condition": {
        "StringEquals": {
          "ec2:InstanceType": ["x1.32xlarge", "p3.16xlarge"]
        }
      }
    }
  ]
}

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "ec2:RunInstances"
      ],
      "Resource": "*",
      "Condition": {
        "StringEquals": {
          "ec2:InstanceType": ["x1.32xlarge", "p3.16xlarge"]
        }
      }
    }
  ]
}

This policy prevents the creation of expensive EC2 instance types across the organization.

Enforcing Tagging Policies

Implement mandatory tagging for cost allocation:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "ec2:RunInstances"
      ],
      "Resource": "arn:aws:ec2:*:*:instance/*",
      "Condition": {
        "StringNotLike": {
          "aws:RequestTag/CostCenter": "*"
        }
      }
    }
  ]
}

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "ec2:RunInstances"
      ],
      "Resource": "arn:aws:ec2:*:*:instance/*",
      "Condition": {
        "StringNotLike": {
          "aws:RequestTag/CostCenter": "*"
        }
      }
    }
  ]
}

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "ec2:RunInstances"
      ],
      "Resource": "arn:aws:ec2:*:*:instance/*",
      "Condition": {
        "StringNotLike": {
          "aws:RequestTag/CostCenter": "*"
        }
      }
    }
  ]
}

This policy ensures that all EC2 instances are tagged with a “CostCenter” tag at creation.

Restricting Expensive Services

Prevent access to services with high cost potential:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "sagemaker:*",
        "dlm:*"
      ],
      "Resource": "*"
    }
  ]
}

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "sagemaker:*",
        "dlm:*"
      ],
      "Resource": "*"
    }
  ]
}

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "sagemaker:*",
        "dlm:*"
      ],
      "Resource": "*"
    }
  ]
}

This policy blocks all actions related to SageMaker and Data Lifecycle Manager, which can incur significant costs if not properly managed.

Preventing Unintended Cost Escalation

Implement guardrails against accidental overspending:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "ec2:ModifyReservedInstances",
        "ec2:PurchaseReservedInstancesOffering"
      ],
      "Resource": "*"
    }
  ]
}

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "ec2:ModifyReservedInstances",
        "ec2:PurchaseReservedInstancesOffering"
      ],
      "Resource": "*"
    }
  ]
}

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": [
        "ec2:ModifyReservedInstances",
        "ec2:PurchaseReservedInstancesOffering"
      ],
      "Resource": "*"
    }
  ]
}

This policy prevents modifications or purchases of Reserved Instances, which require careful financial planning.

Best Practices for SCP Management

Gradual Implementation Strategy

• Start with a small set of non-intrusive policies

• Gradually expand coverage as you assess impact

• Communicate changes to affected teams and stakeholders

Regular Policy Reviews and Updates

• Schedule periodic reviews of SCP effectiveness

• Update policies to align with evolving business needs

• Remove obsolete restrictions to prevent operational bottlenecks

Testing and Validation Processes

• Use AWS Policy Simulator to test SCPs before deployment

• Implement SCPs in a test environment before production

• Monitor AWS CloudTrail logs to verify policy enforcement

Balancing Security and Flexibility

• Avoid overly restrictive policies that hinder innovation

• Implement exception processes for justified policy overrides

• Maintain a balance between cost control and operational agility

SCPs and Cloud Financial Management

Role in Enforcing Budgetary Constraints

SCPs act as a powerful tool for enforcing budget limits by:

• Preventing the creation of resources beyond allocated budgets

• Restricting access to services not included in approved spending plans

• Enforcing cost-saving measures across the organization

Supporting Multi-Account Strategies

In multi-account AWS environments, SCPs facilitate:

• Consistent policy enforcement across all accounts

• Tailored permissions for different account types (e.g., development, production)

• Centralized control over decentralized account structures

Enhancing Cost Allocation and Chargeback

SCPs contribute to improved cost management by:

• Enforcing tagging policies for accurate cost attribution

• Preventing unauthorized resource usage that complicates chargeback

• Supporting the implementation of shared responsibility models

Alignment with FinOps Principles

SCPs align with core FinOps principles by:

• Enabling centralized control over cloud spend

• Promoting accountability through enforced tagging and access controls

• Supporting continuous optimization of cloud resources

Challenges and Considerations

Potential Impact on Operational Workflows

• SCPs may inadvertently block legitimate workflows

• Teams may need to adjust processes to comply with new restrictions

• Careful planning is required to minimize disruption

Overcoming Resistance to Policy Enforcement

• Communicate the benefits of SCPs to all stakeholders

• Provide clear documentation and guidance on policy impacts

• Establish a feedback loop for addressing concerns and exceptions

Maintaining Visibility Across the Organization

• Implement comprehensive logging and monitoring

• Use AWS Config to track compliance with SCPs

• Regularly review and report on policy effectiveness

Scaling SCP Management in Large Environments

• Develop a standardized approach to policy creation and management

• Utilize AWS Organizations APIs for programmatic policy updates

• Implement version control for SCP management

Maximizing Value: SCPs in Your FinOps Strategy

Integration with Other AWS Cost Management Tools

Combine SCPs with:

• AWS Cost Explorer for detailed spend analysis

• AWS Budgets for proactive cost monitoring

• AWS Cost and Usage Report for comprehensive cost data

Measuring the Financial Impact of SCPs

• Track cost trends before and after SCP implementation

• Monitor compliance violations and associated cost savings

• Quantify the reduction in unauthorized or inefficient resource usage

Future Trends and Developments

Stay informed about:

• Enhancements to SCP functionality in AWS Organizations

• Integration with AI-driven cost optimization tools

• Evolving best practices in cloud financial management

Continuous Optimization of SCP Implementation

• Regularly assess the effectiveness of existing policies

• Adapt SCPs to changing business requirements and AWS service offerings

• Leverage community knowledge and shared experiences for improvement

Frequently Asked Questions (FAQs)

What is the primary purpose of AWS Service Control Policies?

AWS SCPs are designed to set guardrails on permissions across multiple AWS accounts within an organization, helping to enforce compliance, security, and cost control measures.

How do SCPs differ from IAM policies?

While IAM policies grant permissions to specific users or roles, SCPs set the maximum permissions available to any entity within an AWS account or organizational unit.

Can SCPs be used to grant permissions?

No, SCPs cannot grant permissions. They can only restrict the maximum available permissions set by IAM policies.

How do SCPs impact root users?

SCPs affect all users and roles in an account, including the root user. However, they do not affect service-linked roles.

Can SCPs be applied to individual IAM users or roles?

No, SCPs can only be applied at the organization, organizational unit, or account level within AWS Organizations.

How can I test SCPs before applying them to my organization?

You can use the AWS Policy Simulator to test the effects of SCPs before implementation, and apply them to test accounts or OUs before wider deployment.