Not sure if you mean maintainability/ability to add future stuff. With that in mind for me it's to do some form of breaking things up so the side effects/remembering is low. Sucks to make a change and have to remember how everything works. In this case tests are nice for regression.
What is your definition of front end that it needs scaling? What is your setup that a proxy and CDNs aren’t enough scalability for a front end? I haven’t encountered a case where the front end is ever the scaling bottleneck so I have to assume that if it is in your case you either are doing something novel or you are defining something that is usually back end as front end.