AWS Cloudformation parameter dependency

Question

I\'m trying to do the following:

\"Parameters\": {
    \"InterfaceMode\" : {
        \"Description\": \"Configure instance to run in onearm or inline mode\",
           


        

Answer 1

Unfortunately, if you want a Parameter to be optional, you can not use any of the AWS-specific parameter types (i.e. AWS::*). None of your hoped-for workarounds will work, either. I'd recommend a type String with an AllowedPattern set to something like ^(subnet-[0-9a-fA-F]{8})?$, but this will not meet your requirement of making the drop-down prepopulated with existing subnet values.