Server WP on multiple servers, wp admin on single db/server

Problem:

Want to run busy wordpress site(s) on multiple server nodes (typical LAMP stack). I want the blogs to be pointed to a single database node (not localhost). Content to public would be served from n server nodes but updates to be done on single instance.

Need wordpress admin/dashboard to be served off of single node pointing to a single database instance. Single node can either be public or internal DNS, though if you can set up one you can do the other. I have complete control over apache, mysql, rsync scripts, php, etc. but I’d like to contain this within apache as much as possible for simplicity’s sake (read: I don’t want to have to compile new php modules or apache modules if possible).

Why does it seem so hard to do this and why is there nothing that I can find easily on the wordpress support site? I can’t be the only person wanting to do this….

Use case:

User logins to dashboard, uploads images which get rsynced from single box to multiple boxes/servers.
Updates blog posts which is pointed to single database.

How can I get this done easily? I am thinking of adding in a redirect for /wp-admin/ to point to https://admin.somesite.com which is a virtual host with internal DNS pointed