Who says the sharded webheads and databases have to be on different boxes? As for the linking problem: I had assumed (wrongly, perhaps) that the application i

Who says the sharded webheads and databases have to be on different boxes? As for the linking problem: I had assumed (wrongly, perhaps) that the application in question is one that is friendly to sharding- an application where little or nothing is shared amongst discrete groups of users (companies, teams, etc) and things are sharded at the group level and not the user level. If the application can't handle that, then sharding is probably not the best database scaling option.