not sure how long ago you tried it out, but ansible has an ec2 inventory script bundled along with it, that you can use instead of maintaining static manifests. This script plugs into the AWS API to get you a list of instances and metadata. Along with that, comes all the goodness of tags and pattern matching, so you can do stuff like tag_Name_DB*:&tag_type_slave to select all database slaves (if you had tags called "Name" and "type" for example)