Building our first environment in the cloud, or perhaps migrating our first couple of workloads to the cloud is fairly easy until we begin the ongoing maintenance of the environment.

Pretty soon we start to realize we are losing control over our environment – from configuration changes, forgetting to implement security best practices, and more.

At this stage, we wish we could have gone back, rebuilt everything from scratch, and have much more strict rules for creating new resources and their configuration.

Manual configuration simply doesn't scale.

Developers would like to focus on what they do best – developing new products or features, while security teams would like to enforce guard rails, allowing developers to do their work, while still enforcing security best practices.

In the past couple of years, one of the hottest topics is called Infrastructure as Code, a declarative way to deploy new environments using code (mostly JSON or YAML format).

Infrastructure as Code is a good solution for deploying a new environment or even reusing some of the code to deploy several environments, however, it is meant for a specific task.

What happens when we would like to set guard rails on an entire cloud account or even on our entire cloud organization environment, containing multiple accounts, which may expand or change daily?

This is where Policy as Code comes into the picture.

Policy as Code allows you to write high-level rules and assign them to an entire cloud environment, to be effective on any existing or new product or service we deploy or consume.

Policy as Code allows security teams to define security, governance, and compliance policies according to business needs and assign them at the organizational level.

The easiest way to explain it is – can user X perform action Y on resource Z?

A more practical example from the AWS realm – block the ability to create a public S3 bucket. Once the policy was set and assigned, security teams won't need to worry whether or not someone made a mistake and left a publicly accessible S3 bucket – the policy will simply block this action.

Looking for a code example to achieve the above goal? See:
https://aws-samples.github.io/aws-iam-permissions-guardrails/guardrails/scp-guardrails.html#scp-s3-1

Policy as Code on AWS

When designing a multi-account environment based on the AWS platform, you should use AWS Control Tower.

The AWS Control Tower is aim to assist organizations deploying multiple AWS accounts under the same AWS organization, with the ability to deploy policies (or Service Control Policies) from a central location, allowing you to have the same policies for every newly created AWS account.

Example of governance policy:

• Enabling resource creation in a specific region – this capability will allow European customers to restrict resource creation in regions outside Europe, to comply with the GDPR. https://docs.aws.amazon.com/organizations/latest/userguide/orgs_manage_policies_scps_examples_general.html#example-scp-deny-region
• Allow only specific EC2 instance types (to preserve cost). https://docs.aws.amazon.com/organizations/latest/userguide/orgs_manage_policies_scps_examples_ec2.html

Example of security policies:

• Prevent upload of unencrypted objects to S3 bucket, to protect access to sensitive objects. https://aws-samples.github.io/aws-iam-permissions-guardrails/guardrails/scp-guardrails.html#scp-s3-2
• Deny the use of the Root user account (least privilege best practice). https://docs.aws.amazon.com/organizations/latest/userguide/orgs_manage_policies_scps_examples_general.html#example-scp-root-user

AWS Control Tower allows you to configure baseline policies using CloudFormation templates, over an entire AWS organization, or on a specific AWS account.

To further assist in writing CloudFormation templates and service control policies on large scale, AWS offers some additional tools:

Customizations for AWS Control Tower (CfCT) – ability to customize AWS accounts and OU's, make sure governance and security policies remain synched with security best practices.

AWS CloudFormation Guard – ability to check for CloudFormation templates compliance against pre-defined policies.

Summary

Policy as Code allows an organization to automate governance and security policies deployment on large scale, keeping AWS organizations and accounts secure, while allowing developers to invest time in developing new products, with minimal required changes to their code, to be compliant with organizational policies.

References

• Best Practices for AWS Organizations Service Control Policies in a Multi-Account Environment https://aws.amazon.com/blogs/industries/best-practices-for-aws-organizations-service-control-policies-in-a-multi-account-environment/
• AWS IAM Permissions Guardrails https://aws-samples.github.io/aws-iam-permissions-guardrails/guardrails/scp-guardrails.html
• AWS Organizations – general examples https://docs.aws.amazon.com/organizations/latest/userguide/orgs_manage_policies_scps_examples_general.html
• Customizations for AWS Control Tower (CfCT) overview https://docs.aws.amazon.com/controltower/latest/userguide/cfct-overview.html
• Policy-as-Code for Securing AWS and Third-Party Resource Types https://aws.amazon.com/blogs/mt/policy-as-code-for-securing-aws-and-third-party-resource-types/