AWS Cloudformation list parameter for array type fails - aws-cloudformation

Question

I'm creating a cloudfront distro with cloudformation and trying to use parameters to populate the aliases.
If I use a single string, it fails because it wants a list. And if I use a list, it fails because it wants an array.
For example, this works (no params):
<!-- language: json -->
{
"Resources": {
"FrontEndBucket": {
"Type": "AWS::S3::Bucket",
"Properties": {
"BucketName":"test.tester.huh"
}
},
"CloudFrontDistro": {
"Type": "AWS::CloudFront::Distribution",
"Properties": {
"DistributionConfig": {
"Aliases": ["testalias.tester.huh"],
"Enabled":true,
"Origins": [
{
"DomainName": "test.tester.huh.s3.amazonaws.com",
"Id":"OriginId",
"S3OriginConfig": { }
}
],
"DefaultCacheBehavior": {
"TargetOriginId": "OriginId",
"ViewerProtocolPolicy": "allow-all",
"ForwardedValues": {
"QueryString": true
}
}
}
}
}
}
}
But when I run this:
{
"Parameters" : {
"DomainAliases" : {
"Type" : "CommaDelimitedList"
}
},
"Resources": {
"CloudFrontDistro": {
"Type": "AWS::CloudFront::Distribution",
"Properties": {
"DistributionConfig": {
"Aliases": {"ref":"DomainAliases"},
"Enabled":true,
"Origins": [
{
"DomainName": "test.tester.huh.s3.amazonaws.com",
"Id":"OriginId",
"S3OriginConfig": { }
}
],
"DefaultCacheBehavior": {
"TargetOriginId": "OriginId",
"ViewerProtocolPolicy": "allow-all",
"ForwardedValues": {
"QueryString": true
}
}
}
}
}
}
}
It fails with this:
(*note: it does pass initial validation)
Property validation failure: [Value of property {/DistributionConfig/Aliases} does not match type {Array}]

Answer 1

Looking at the bare minimum requirements for AWS::CloudFront::Distribution and the sample from their page, the following template validated perfectly fine for me:
{
"AWSTemplateFormatVersion": "2010-09-09",
"Parameters": {
"DomainAliases": {
"Type": "CommaDelimitedList"
}
},
"Resources": {
"myDistribution": {
"Type": "AWS::CloudFront::Distribution",
"Properties": {
"DistributionConfig": {
"Aliases": {
"ref": "DomainAliases"
},
"Origins": [{
"DomainName": "mybucket.s3.amazonaws.com",
"Id": "myS3Origin",
"S3OriginConfig": {
"OriginAccessIdentity": "origin-access-identity/cloudfront/E127EXAMPLE51Z"
}
}],
"Enabled": "true",
"DefaultCacheBehavior": {
"AllowedMethods": ["DELETE", "GET", "HEAD", "OPTIONS", "PATCH", "POST", "PUT"],
"TargetOriginId": "myS3Origin",
"ForwardedValues": {
"QueryString": "false",
"Cookies": {
"Forward": "none"
}
},
"TrustedSigners": ["1234567890EX", "1234567891EX"],
"ViewerProtocolPolicy": "allow-all"
}
}
}
}
}
}

Answer 2

I ran into this issue myself. It wants Aliases in an array, not a string. Added some square brackets and that fixed it:
"Properties": {
"DistributionConfig":
{
"Aliases":
[
{
"ref":"DomainAliases"
}
],
}
}