I’d like to setup apostrophe-cms to work on rackspace cloud hosting. Any ideas the best configuration?
We have found that with Digital Ocean for sites with smaller traffic Apostrophe performs very well even on cheaper hosting packages.
Rackspace is one of the most expensive options, but they do provide very high reliability and sometimes it is a client requirement.
A Rackspace VPS is sufficient for all but the most high-traffic projects. VPSes can scale up quite large.
Beyond that, check out these HOWTOs:
http://apostrophecms.org/docs/tutorials/howtos/deploying-apostrophe-in-the-cloud.html
But keep in mind that “true” cloud hosting, with multiple frontend servers, a mongodb replica set, etc. is the most difficult configuration and most of your clients simply don’t need it. (They do, of course, need backups.)