First great article!
Josh Frankel

Josh Frankel no resources really come to my mind right away, but the idea is to migrate your app incrementally/partially. The old version would continue serving your users, while the new would run on a separate server only for your internal use, dogfooding if you will. By making “cluster” ready, I meant you would extract any shared configuration (background processing, database, caching, etc.), so that you could use it in a multi-instance environment. Hope that clears it up ;)