CDK CFN Guard Validator Plugin

The APIs of higher level constructs in this module are experimental and under active development. They are subject to non-backward compatible changes or removal in any future version. These are not subject to the Semantic Versioning model and breaking changes will be announced in the release notes. This means that while you may use them, you may need to update your source code when upgrading to a newer version of this package.

Installing

TypeScript/JavaScript

npm install @cdklabs/cdk-validator-cfnguard

Python

pip install cdklabs.cdk-validator-cfnguard

Java

// add this to your pom.xml
<dependency>
    <groupId>io.github.cdklabs</groupId>
    <artifactId>cdk-validator-cfnguard</artifactId>
    <version>0.0.0</version> // replace with version
</dependency>

.NET

dotnet add package Cdklabs.CdkValidatorCfnGuard --version X.X.X

Usage

To use this plugin in your CDK application add it to the CDK App.

new App({
  policyValidationBeta1: [
    new CfnGuardValidator(),
  ],
});

By default the CfnGuardValidator plugin comes with the Control Tower proactive controls enabled. In order to disable these rules you can use the controlTowerRulesEnabled: false property.

new CfnGuardValidator({
  controlTowerRulesEnabled: false,
});

It is also possible to disable individual rules.

new CfnGuardValidator({
  disabledRules: [
    'ct-s3-pr-1',
  ],
});

Additional rules

To provide additional rules to the plugin, provide a list of local file or directory paths.

new CfnGuardValidator({
  rules: [
    'path/to/local-rules-directory',
    'path/to/s3/local-rules/my-rule.guard',
  ],
});

If the path provided is a directory then the directory must only contain guard rule files, and all rules within the directory will be used.

Using the bundled Control Tower proactive controls in CDK

The bundled Control Tower proactive controls use CloudFormation Guard policies that are also used in managed controls from the Control Tower service. You can use these CDK bundled controls without having a Control Tower environment in AWS, but there are many benefits to using the two together.

When you enable Control Tower proactive controls in your Control Tower environment, the controls can stop the deployment of non-compliant resources deployed via CloudFormation. For more information about managed proactive controls and how they work, see the Control Tower documentation.

These CDK bundled controls and managed Control Tower proactive controls are best used together. In this scenario you can configure this validation plugin with the same proactive controls that are active in your Control Tower cloud environment. You can then quickly gain confidence that your CDK application will pass the Control Tower controls by running cdk synth locally or in a pipeline as described above.

Regardless of whether you or your organization use Control Tower, however, you should understand the following things about these bundled controls when run locally using this plugin:

1. These CloudFormation guard policies accept a limited subset of CloudFormation syntax for the properties they evaluate. For instance, a property called EncryptionEnabled may pass if it is specified with the literal value true, but it may fail if it is specified with a reference to a CloudFormation stack parameter instead. Similarly, if a rule checks for a string value, it may fail for Fn::Join objects. If you discover that a rule can be bypassed with a particular configuration of a resource, please file an issue.
2. Some rules may check references to other resources, but this reference checking is limited. For instance, a rule may require that an access logging bucket is specified for each S3 bucket. In this case, the rule can check whether you have passed a reference to a bucket in the same template, but it cannot verify that a hardcoded bucket name like "examplebucket" actually refers to a real bucket or a bucket you own.

You can add a layer of security protection by enabling the same proactive controls in your Control Tower cloud environment. There are different considerations for using these controls since they operate in a different way. For more information, see the Control Tower proactive controls documentation.

If you do not yet have a Control Tower environment, see What is AWS Control Tower?.

Bundled Control Tower Rules