Hello, I have a new project in mind, but it has some pretty nasty requirements (scalability)..

To clarify what it's about, it's basically going to be a service where people can make their own website.

All files (php..) are hosted on one server, so basically all website's are going to be the same, however each website has it's own preferences, like custom layout, stuff like that.
These preferences are saved in a seperate mysql database (each website has it's own database) spread over several servers, to ensure it will run smooth in the future.

- File server 1
- Database servers 1-9

Website 1:
Fileserver 1
Db server 1

Website 2:
Fileserver 1
Db server 2

etc..

Just to give you a picture. Of course I won't be having a whole database server for each website, like 100 databases will be hosted per server.

Now my real question is, is something like this even possible?
I understand there has to be some sort of a gateway/load balancer for each website, so it knows which DB server to use, but I don't have the slightest idea how to start with this..

If it all can be done on 1 server, that'd be even better, but as the amount of websites will increase, I don't want to rely on one single server.


Can anyone please inform (if you have experience with high scalability services)?

Thanks