Evaluating Resources with AWS Config Rules

Use AWS Config to evaluate the configuration settings of your AWS resources. You do this by creating AWS Config rules, which represent your ideal configuration settings. AWS Config provides customizable, predefined rules called managed rules to help you get started.

How AWS Config Rules Work

While AWS Config continuously tracks the configuration changes that occur among your resources, it checks whether these changes do not comply with the conditions in your rules. If a resource does not comply with rule, AWS Config flags the resource and the rule as noncompliant.

There are four possible evaluation results for an AWS Config rule.

For example, when an EC2 volume is created, AWS Config can evaluate the volume against a rule that requires volumes to be encrypted. If the volume is not encrypted, AWS Config flags the volume and the rule as noncompliant. AWS Config can also check all of your resources for account-wide requirements. For example, AWS Config can check whether the number of EC2 volumes in an account stays within a desired total, or whether an account uses AWS CloudTrail for logging.

Service-linked Rules

Service-linked rules are a unique type of managed rule that support other AWS services to create AWS Config rules in your account. These rules are predefined to include all the permissions required to call other AWS services on your behalf. These rules are similar to standards that an AWS service recommends in your AWS account for compliance verification. For more information, see Service-Linked AWS Config Rules.

Custom Rules

You can also create custom rules to evaluate additional resources that AWS Config doesn't yet record. For more information, see AWS Config Custom Rules and Evaluating Additional Resource Types.

Viewing Compliance

The AWS Config console shows the compliance status of your rules and resources. You can see how your AWS resources comply overall with your desired configurations, and learn which specific resources are noncompliant. You can also use the AWS CLI, the AWS Config API, and AWS SDKs to make requests to the AWS Config service for compliance information.

By using AWS Config to evaluate your resource configurations, you can assess how well your resource configurations comply with internal practices, industry guidelines, and regulations.

Limits

For the maximum number of AWS Config rules for each Region for each account and other service limits, see AWS Config Service Limits.

Cost Considerations

For details about the costs associated with resource recording, see AWS Config pricing.

Recommendation: Consider excluding the AWS::Config::ResourceCompliance resource type from recording before deleting rules

Deleting rules creates configuration items (CIs) for AWS::Config::ResourceCompliance that can affect your costs for the configuration recorder. If you are deleting rules which evaluate a large number of resource types, this can lead to a spike in the number of CIs recorded.

To avoid the associated costs, you can opt to disable recording for the AWS::Config::ResourceCompliance resource type before deleting rules, and re-enable recording after the rules have been deleted.

However, since deleting rules is an asynchronous process, it might take an hour or more to complete. During the time when recording is disabled for AWS::Config::ResourceCompliance, rule evaluations will not be recorded in the associated resource’s history.

AWS Config recommends that you weigh these factors on a case-by-case basis before deciding how to proceed with deleting rules.

Recommendation: Add logic to handle the evaluation of deleted resources for custom lambda rules

When creating AWS Config custom lambda rules, it is highly recommended that you add logic to handle the evaluation of deleted resources.

When evaluation results are marked as NOT_APPLICABLE, they will be marked for deletion and cleaned up. If they're NOT marked as NOT_APPLICABLE, the evaluation results will remain unchanged until the rule is deleted, which can cause an unexpected spike in the creation of CIs for AWS::Config::ResourceCompliance upon rule deletion.

For information on how to set AWS Config custom lambda rules to return NOT_APPLICABLE for deleted resources, see Managing deleted resources with AWS Config custom lambda rules.

Recommendation: Provide the resources in scope for custom lambda rules

AWS Config Custom Lambda Rules can cause a high number of Lambda function invocations if the rule is not scoped to one or more resource types. To avoid increased activity associated with your account, it is highly recommended to provide resources in scope for your Custom Lambda rules. If no resource types are selected, the rule will invoke the Lambda function for all resources in the account.

Region Support

Currently, the AWS Config Rule feature is supported in the following AWS regions. For a list of which individual AWS Config rules are supported in which Regions, see List of AWS Config Managed Rules by Region Availability.

Deploying AWS Config Rules across member accounts in an AWS Organization is supported in the following Regions.