A client error (ValidationError) occurred when calling the CreateStack operation: Template error: variable names in Fn::Sub syntax must contain only alphanumeric characters, underscores, periods, and colons
The error seems straightforward but it is not exactly accurate, because the UserData section also allows things like # for comments, single quotes, and other characters. I whittled it down to disallowing the curly braces I was attempting to use based on other web sites that are obviously incorrect.
