Enumerating AWS instances in Rails, with error handling
The rescue in your fetch_aws_instances method is pointless. Rescuing errors just to re-raise them identically, is the same as not rescuing them at all. 

You should only rescue when you want to customize what happens if the error is raisedd. Unless you want to move the Rails.logger calls to the fetch_aws_instances method, you should only have the rescues when you call it (as you do in your second code block)