Yes, all of this was designed with overlayfs in mind. I am waiting anxiously for Linux Kernel 3.18 to land, this is a huge step forward for Linux and years in the making.

Cool! The idea of filesets is very nice - there are some very interesting workflow ideas buried in there. I've been looking forward to a mainstream unioning filesystem for a while too - and I hope rocket does some serious exploration (or enables it) of how to take advantage of them fully in both development and deployment. (And while I'm at it, testing too).

My personal wish-list down this path includes:

* options in the relevant manifests on which layer is writable ... if I'm doing development on libfoo which is used by several different apps, let me make that layer writable so I can rapidly iterate integration tests and (bad practice) live coding on testing/dev servers.

* tools to help me smash a dev layer or 3 into a single fileset (and similarly dissect a layer into a few new filesets during a refactoring)

* the ability to use filesets and overlays in a way similar to package management is now, but with extended features that are similar to python's virtualenv.

One of the things I see as a boon of the filesets as described is: I can update parts of my system without having to rebuild the whole dang app silo from the get go. Combining this with some of the above features looks like it could be useful for making "thin" images - where I can build all my code in one place, and port only the binaries to the staging and deployment images, just by doing a few fileset/overlay tricks. (no more complicated scripts)

Whether Velociraptor uses Rocket or not, implementing the App Container Spec seems like a no brainer. I've made https://bitbucket.org/yougov/velociraptor/issue/136.