Working example of AWS::EC2::TransitGatewayMulticastDomainAssociation?

Question

I have run into something that I could use some help with: I'm trying to setup an Cloudformation template for a VPC with support for multicasting, and I have it except for the AWS::EC2::TransitGatewayMulticastDomainAssociation which forms the "last mile" connection. That resource type seems to have some contradictory information in the documentation1, which has the property named SubnetId (singular) and String type that's described as holding multiple subnets. I need three subnets associated with the multicast domain and I'm not sure how to accomplish that. As far as I can tell from searching github, there are no public examples of using this resource type.

Help?

[1]: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-ec2-transitgatewaymulticastdomainassociation.html

Accepted Answer

What if we create an "AWS::EC2::TransitGatewayMulticastDomainAssociation" for each subnet?  
```
  Association1:
    Type: AWS::EC2::TransitGatewayMulticastDomainAssociation
    Properties: 
      SubnetId: !Ref Subnet1
      TransitGatewayAttachmentId: !Ref TransitGatewayAttachment
      TransitGatewayMulticastDomainId: !Ref TransitGatewayMulticastDomain

Association2:
    Type: AWS::EC2::TransitGatewayMulticastDomainAssociation
    Properties: 
      SubnetId: !Ref Subnet2
      TransitGatewayAttachmentId: !Ref TransitGatewayAttachment
      TransitGatewayMulticastDomainId: !Ref TransitGatewayMulticastDomain

Association3:
    Type: AWS::EC2::TransitGatewayMulticastDomainAssociation
    Properties: 
      SubnetId: !Ref Subnet3
      TransitGatewayAttachmentId: !Ref TransitGatewayAttachment
      TransitGatewayMulticastDomainId: !Ref TransitGatewayMulticastDomain
```

Working example of AWS::EC2::TransitGatewayMulticastDomainAssociation?

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