How to get the target domain name of a custom domain for Regional AWS API Gateway in Cloudformation?

Question

I'm trying to create a multi-region serverless application on AWS. I've followed the instructions given here. I'm using Serverless framework, which uses Cloudformation scripts for creating all the resources on AWS.

I want to create a custom domain for API gateway as a Regional Endpoint. When it creates a Regional endpoint, it generates a target domain. I would like to know how can I get the value of the target domain in my Cloudformation script?

When I create an Edge optimized Endpoint, I get the value of the CloudFront deployment by using the DistributionDomainName attribute. But I don't see any attribute for the target domain name when a Regional Endpoint is created. I tried using the DistributionDomainName attribute for a Regional endpoint, but it throws an error which says that there is no DistributionDomainName.

Below is a part of my script -

# Creates a custom domain for the ApiGateway
customDomain:
  Type: 'AWS::ApiGateway::DomainName'
  Properties:
    DomainName: ${self:custom.domain}
    EndpointConfiguration:
      Types:
        - REGIONAL
    RegionalCertificateArn: ${self:custom.certificateArn}

# Insert a DNS record in route53 hosted zone to redirect from the custom domain to CF distribution
dnsRecord:
  Type: AWS::Route53::RecordSet
  Properties:
    Region: ${self:provider.region}
    SetIdentifier: ${self:provider.region}
    HostedZoneId: ${self:custom.hostedZoneId}
    Name: ${self:custom.domain}
    Type: CNAME
    TTL: 60
    ResourceRecords:
      - "Fn::GetAtt": [customDomain, DistributionDomainName]

Please help. Thanks!

UPDATE

Cloudformation now returns the regional domain name through RegionalDomainName property. It could be used as Fn:GetAtt : [customDomain, RegionalDomainName].

Answer 1

This is not possible at the moment.

As you mentioned, the only exposed parameter is DistributionDomainName and this works only for edge-optimized endpoints.

As a workaround (until it will be implemented in CloudFormation) you could use a CustomResource backed up by your own Lambda function to return the regionalDomainName attribute.

Here's a sample CloudFormation YAML code that does this:

Resources:
  # The workaround Lambda that returns the regionalDomainName property
  RegionalDomainLambda:
    Type: AWS::Lambda::Function
    Properties:
      Runtime: python2.7
      Handler: index.handler
      Role:
        'Fn::GetAtt': [YOUR_ROLE_GOES_HERE, Arn] # make sure you include apigateway:GET
      Timeout: 50
      Code:
        ZipFile: |
          import cfnresponse
          import json
          import boto3

          client = boto3.client('apigateway')
          def handler(event, context):
              response_data = {}
              try:
                  domainName = event['ResourceProperties']['DomainName']
                  regional_domain_name = client.get_domain_name(domainName=domainName)['regionalDomainName']
                  response_data['value'] = regional_domain_name

                  cfnresponse.send(event, context, cfnresponse.SUCCESS,response_data, "RegionalDomainNameString")
              except Exception as e:
                  response_data['exception'] = e
                  cfnresponse.send(event, context, cfnresponse.FAILED, response_data, "RegionalDomainNameString")

  # The resource that serves as a placeholder
  RegionalDomain:
    Type: Custom::CustomResource
    Properties:
      ServiceToken:
        'Fn::GetAtt': [RegionalDomainLambda, Arn]
      DomainName: {Ref: YOUR_API_GATEWAY_DOMAIN_NAME_GOES_HERE}

  # And here's how to use it
  SomeOtherResource:
    SomeOtherProperty: {'Fn::GetAtt': [RegionalDomain, value]}