Problem

Amazon has enabled entire companies to be created around specific shortcomings in their platform. Serverless, a framework that facilitates seamless deployments of AWS Lambda functions, addresses the chicken and egg problem when deploying a CloudFormation stack that defines an AWS Lambda function and the S3 bucket in which it resides.

Similarly, the process of creating and validating an AWS Certificate Manager (ACM) certificate via CloudFormation is equally cumbersome. The AWS::CertificateManager::Certificate resource requests an ACM certificate that you can use to enable secure connections. However, when you use the AWS::CertificateManager::Certificate resource in an AWS CloudFormation stack, the stack will remain in the CREATE_IN_PROGRESS state until you validate the certificate request. Further stack operations will be delayed until acting upon the instructions in the validation email or by adding a CNAME record to your DNS configuration.

Both options break a fully automated deployment pipeline as they require manual intervention. Additionally, if email validation is used for a certificate, to renew the certificate, a renewal email must be acted upon as well. If more than 72 hours have elapsed since you received the validation email, the certificate will expire and you will have to request a new certificate. As browsers move toward restricting access to domains not secured by TLS, this can have serious consequences for a website, service or application that uses an ACM certificate.

Solution

As previously stated, an AWS::CertificateManager::Certificate resource can be validated via email or DNS. Email validation is problematic, since it is difficult to automate and introduces additional points of failure to a system. DNS validation, however, has its own automation issues. One could manually create the CNAME records in the AWS Management Console (Certificate Manager > Create record in Route 53), but this defeats the purpose of automation. You could also write a script to retrieve the CNAME record name and value from the CloudFormation stack events, but this option is limited by the fact that AWS CloudFormation only returns the CNAME record for the domain specified by the DomainName property of the AWS::CertificateManager::Certificate resource, so forget about validating any additional fully qualified domain names (FQDNs) given under the SubjectAlternativeNames property for the certificate.

This is where Certificate Validator comes in.

What is Certificate Validator?

Certificate Validator is an AWS CloudFormation custom resource which facilitates ACM certificate validation via DNS. A custom resource allows you to write custom provisioning logic in templates that AWS CloudFormation runs anytime you create, update or delete stacks. A custom resource is basically an abstraction of every concrete AWS CloudFormation resource. However, you, the developer, are now responsible for its lifecycle.

At its core, Certificate Validator is an AWS Lambda function that handles the creation and validation of an ACM certificate. It accomplishes this without stopping the execution of the CloudFormation deployment and automatically creates the record sets in Route53 that are used to validate the ACM certificate.

Getting Started

It is extremely easy to get started with Certificate Validator. Simply deploy Certificate Validator and add the Custom::Certificate and Custom::CertificateValidator custom resources to your AWS CloudFormation templates.

Check out the Getting Started documentation for a full guide.

Conclusion

Using custom resources, an enterprising developer can fill the gaps left by AWS CloudFormation. Certificate Validator removes the manual process of clicking an email or going out to the AWS Management Console to validate a certificate, which increases automation and improves security and reliability.

Certificate Validator is fully open-source. If you would like to contribute to its development, please read the Contributing documentation. If you would like to report bugs, request features or submit feedback, create an issue.

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