We are just getting into cloud computing in a big way but the main problem has been spooling new machines up in a clean and repeatable way. Our current thought

We are just getting into cloud computing in a big way but the main problem has been spooling new machines up in a clean and repeatable way. Our current thought is to boot up a "raw" AMI and use Puppet to provision it. CloudFormation might be a better way. Instead of having Puppet maintain the system, why not just update the CF template and spool up a new instance to replace the old, outdated one? I guess it just depends on how much you can stick in a template. If you can specify specific versions of packages (Ruby 1.9.2) it might just work.