Can someone explain how this (or other tools like this?) work? How do they install services, ensure they start up, handle upgrades, etc? I am utterly confused by all these PaaSaaS apps.
Scaling your app simply means having more running dynos that are load balanced by a centralised load balancer used across the entire platform. So yes, interestingly there is a lot of duplication of the code base.
Services, like databases, are managed on their own separate servers/clusters and allow multiple connections and can be scaled/sharded separately from the dyno farms. Therefore they can be monitored, maintained, upgraded, etc, separately as well.
I'm a small-time contributor to http://github.com/openruko, an opensource Heroku clone.
PaaS is "platform as a service". A way of automatically deploying, updating, and managing applications inside of application containers running on a cluster of machines, using either processes, virtualization, or OS-level process containers.
Amazon BeanStalk does this for Java by using Tomcat running in a EC2 VM, and exposing the servlet interface such that one can deploy Java webapps directly to BeanStalk.
Google App Engine did the same thing for Java, and with some custom packaging for Python.
The whole idea is to get rid of all the textual OS configuration files and vestigal limbs of UNIX and get down to the simple bare metal fact that we tend to treat the OS as a hardware abstraction layer for a single application.
I guess this ties in with another post I saw the other day, which was a lightweight container format you could add your environment to and deploy (and sounds like a game-changing idea). If we have a functional, standardized, self-contained container format that provides reasonable security and that you can install an environment to and just deploy to a server, it would pretty much mean that you can pick your app up and copy it to another host and be running in five minutes.