This depends a <i>lot</i> on your software design.  You have to shed a lot of assumptions before you can even begin to consider redundancy.  If your software can only run on one computer, then nothing much matters.<p>It would be a worthwhile experiment to see what it'd take to get your site running on GAE or perhaps heroku.  In both cases, you are sufficiently constrained such that front-end scalability is trivial, and backend redundancy is managed for you.<p>Of course, many of us have done this ourselves, but these days I'd rather just get it in a box where I'm doing something fairly small (i.e. could even run on one computer).