[bmoyles]

A combination of things such as Spinnaker providing granular environmental context to an instance by way of user data (things that the ec2 metadata service doesn't readily provide to an instance without API calls), dynamic properties which can be controlled down to the instance-level (http://techblog.netflix.com/2012/06/annoucing-archaius-dynam... ), and other solutions depending on a team's needs.