You seem to be describing essentially a static allocation of dedicated machines. That's fine if there are a couple of different apps you want to run. It'd be to

You seem to be describing essentially a static allocation of dedicated machines. That's fine if there are a couple of different apps you want to run. It'd be totally insane if a single data centre has 10k+ servers that are permanently running hundreds of different services and thousands of largely unpredictable and transient batch jobs. (Why would it be insane? Because with dedicated machines your utilization levels are going to be crap, reconfiguring and rebalancing the machine allocations will be painful, and you'd need massive over-provisioning to achieve a sufficient level of fault-tolerance.)