cloudformation-samples.md

Multiline yaml sub

      DestinationPolicy: 
        Fn::Sub:
          - |
            {
                "Version" : "2012-10-17",
                "Statement" : [
                    {
                    "Sid" : "",
                    "Effect" : "Allow",
                    "Principal" : {
                        "AWS" : ["${JoinedAccountIds}"]
                    },
                    "Action" : "logs:PutSubscriptionFilter",
                    "Resource" : "arn:aws:logs:us-east-1:767815946864:destination:${Environment}-${Brand}-${Application}-1"
                    }
                ]
            }
          - {
              JoinedAccountIds: !Join ['","', !Ref Test]
            }

Conditions for optional params

Parameters:
  OptionalStringParam:
    Type: String
    Default: ''
  OptionalCommaDelimitedListParam:
    Type: CommaDelimitedList
    Default: ''
Conditions:
  OptionalStringParamHasValue: !Not [!Equals [!Ref OptionalStringParam, ""]]
  OptionalCommaDelimitedListParamHasValue: !Not [!Equals [ !Join [ '', !Ref OptionalCommaDelimitedListParam], '']]