问题
Have a collection of cloudformation templates in a parent-child relationship and want to pass an AWS::IAM::Role into the parameters of a child stack and use GetAttr to get the Arn.
This fails validation because can only call GetAttr on resources, not on parameters.
Anyone know/guess why this is designed in this way?
It's not a problem as it can be worked around by just passing the Arn into the stack, I'm just curious really
回答1:
What Fn::GetAttr and Parameters are trying to do in AWS CloudFormation is fundamentally different. As per AWS docs:
The intrinsic function Fn::GetAtt returns the value of an attribute from a resource in the template.
[1] http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-getatt.html
You can use the optional Parameters section to pass values into your template when you create a stack. With parameters, you can create templates that are customized each time you create a stack.
[2] http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/parameters-section-structure.html
I believe your confusion is stemming from the fact that you're trying to think of this in terms of the object-oriented/some other programming paradigm, where Resources and Parameters are some kind of objects and Fn::GetAttr is a generic function which retrieves the value of a reference that's passed in as an argument.
来源：https://stackoverflow.com/questions/42629914/why-does-getattr-not-work-on-cloudformation-template-parameters