You can use capistrano-chef, a RubyGem that allows you to use Chef Search for role names to do the deployment.
Possibly unrelated, Evan Machnic has a video of how he uses Chef and capistrano from a presentation at a Ruby Brigade meeting.
You can also do a deployment as a resource inside Chef recipes.
Someone blogged about this here:
If you use chef-solo, you don't get to use knife. Knife is API client for the chef-server, with some extra utility sugar (like knife rackspace server create you've mentioned).
To configure server with chef-solo, you should copy your chef repo to the server, and run chef-solo there over ssh. There is no ready-made script or knife plugin that I know of that would do it automatically.
Command knife rackspace server create creates new Rackspace server, and then initializes it for chef-server that knife knows of by calling knife bootstrap. It won't work with chef-solo easily.
Technically, knife bootstrap, and thus knife rackspace server create, can be coerced to work with chef-solo by writing a custom bootstrap template that, instead of initializing chef-client, would download your chef repository and run chef-solo - see knife bootstrap --help, its wiki page, or source for details. You can see example templates for installing chef-client here. This is an advanced feature, though, and it's not very well documented.
If you don't want to handle complexity of installing and managing your own chef-server, you can use free layer of Opscode's Hosted Chef, which is Chef-server SAAS offering and is free up to three nodes. I'd recommend starting any serious work with server anyway - chef-solo is as good as a decent bootstrap shell script, no more, and you're missing out on many important/interesting features like search and data bags, which allow you to configure your servers in a data-driven way.
Best Answer
You can auto scale your EC2 instance. Check this post, but before doing it have read this discussion. I am currently using chef for configure my ec2 instaces and cloudformation for amazon resources set up. Recetly CloudFormation has integrated chef. I am using Cloud formation and chef both and it works well for me.