AWS Certificate Manager is a great service that allows the creation and renewal of certificates to be automated. It provides two ways of validating a certificate request: through email and through DNS.

When you are creating immutable infrastructure, the email validation method is a no-go as it requires human intervention. The DNS validation is of course the way to go! With 'Route53' we have full control over the DNS domain and can create the required records.

Although the CloudFormation AWS::CertificateManager::Certificate resource allow you to specify that you want DNS validation, it does not reveal the DNS records that you need to create. It writes them in the CloudFormation log file so that another human has to collect them and manually update the DNS record.

With this custom provider you can fully automated the creation of certificates with CloudFormation!

As a prerequisite, you need to have the hosted zones for the domain names on your certificate in Route53. If you have that, you can fully automate the provisioning of certificates, with the following resources:

1. Custom::Certificate to request a certificate without waiting for it to be issued
2. Custom::CertificateDNSRecord which will obtain the DNS record for a domain name on the certificate.
3. Custom::IssuedCertificate which will activately wait until the certificate is issued.
4. AWS::Route53::ResourceRecordSet to create the validation DNS record.

Checkout the sample in cloudformation/demo-stack.yaml.

To install this custom resource, type:

aws cloudformation deploy \
        --capabilities CAPABILITY_IAM \
	--stack-name cfn-certificate-provider \
	--template-file cloudformation/cfn-resource-provider.yaml

This CloudFormation template will use our pre-packaged provider from s3://binxio-public-${AWS_REGION}/lambdas/cfn-certificate-provider-0.2.4.zip.

To install the simple sample of the Custom Resource, type:

read -p "domain name: " DOMAIN_NAME
read -p "hosted zone id: " HOSTED_ZONE
aws cloudformation deploy --stack-name cfn-certificate-provider-demo \
	--template-file cloudformation/demo-stack.yaml \
	--parameter-overrides DomainName=$DOMAIN_NAME HostedZoneId=$HOSTED_ZONE