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

I've been looking for this type of conditional parameter as well and as far as I can tell it doesn't exist. The closest you can come is an AWS Condition.

http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/conditions-section-structure.html http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-conditions.html

This will allow you to define conditions that evaluate to true or false based on input parameters that you can then use along with Fn:If statements to inject different values into resources.

So for your above scenario you may want to default the value to a known subnet id, but use Conditions to ignore this value if not needed. Unfortunately this falls a bit short if you are trying to use the same CloudFormation template across different VPCs as the default subnet wouldn't exist.