Using puppet when configuring EC2 machines seems a natural fit. However bringing up new machines from a community image with puppet is not trivial and can be slow, and so not useful for auto-scaling.
The cloud also offers a solution to ongoing server maintenance, allowing you to launch fresh instances whenever you upgrade your applications (Immutable or Phoenix servers). However to predictably succeed, you need to freeze the puppet code alongside the application version for deployment.
The solution to these issues is generating custom machine images (AMIs) with your software inlined. This talk will cover Yelp's use of a Packer, Jenkins and Puppet for generating AMIs. This will include how we deal with issues like bootstrapping, getting canonical information about a machine's environment and cluster state at launch time, as well as supporting immutable/phoenix servers in combination with more traditional long lived servers inside our hybrid cloud infrastructure.